Classification of Hiking Difficulty Levels of Accessible Natural Trails

Abstract

The accessibility of nature trails for people with motor disabilities and impairments stands as a significant challenge for inclusive tourism. In the present study, we would like to present a review of research, approaches, and solutions to enable people with motor impairments to enjoy nature trails independently or with assistance. The study is conducted from the perspective of public bodies that aim to reduce the accessibility barriers for People with Disabilities (PwDs) by adapting and improving the conditions of the trails and by providing clear and comprehensive information about the difficulties that hikers may encounter on a trail while using a specific aid. The paper initially presents the wide variety of aids for outdoor mobility, including both those to be used independently (i.e., self-propelled wheelchairs that can be equipped with additional small wheels, off-road wheels and/or auxiliary drives) and those that require assistance (e.g., single-wheeled wheelchairs). Then, we shift focus onto the difficulty classification of trails for PwDs, analysing papers and guidelines that tried to define objective evaluation criteria such as the slope, the trail surface, and the length of the sloping sections. Starting from these studies, the paper proposes a synthesis of the different classifications that consider, for the first time, all the aids available on the market, thus filling the gaps of the single studies. In the last sections, we present some national and international guidelines with tailored and practical solutions to improve the accessibility of nature trails and some studies about the inclusive planning that directly involves PwDs, as well as on the need for a better training of tourism service providers. The present work aims to stimulate a debate on the barriers and opportunities related to the accessibility of hiking trails, contributing to making nature a truly accessible experience for all.

1. Introduction

Scientific interest in the relationship between tourism and disability has grown significantly, with a marked acceleration since the 2000s [1]. In this scenario, the interpretation of tourism as a fundamental human right places access to tourist experiences at the centre of citizenship and social inclusion processes [2]. At the same time, the therapeutic perspective emphasises how accessible tourism can serve as a key resource for stress management and improving the psychological well-being of PwDs [3]. Confirming this evidence, caregivers’ perceptions also show that participation in tourist activities not only promotes accessibility and inclusion, but also generates multidimensional benefits ranging from increased self-confidence to the development of social skills [4].

Within this general framework, this paper focuses on outdoor tourism, with particular attention paid to the accessibility of natural spaces for PwDs, especially those with motor disabilities. This is an increasingly important issue in the field of inclusive tourism. Interaction with nature is a fundamental element for the well-being of each individual, and more and more studies confirm that visiting green spaces, such as parks and trails, brings significant benefits to mental and physical health [5,6]. However, people with motor disabilities continue to visit such spaces less frequently than non-disabled people [7,8,9], highlighting a critical need to improve the accessibility of natural areas.

In this context, accessible hiking, understood as the possibility for people with motor disabilities to enjoy nature trails independently or with assistance, is a challenge that has not been fully addressed yet. This study is part of the debate on how to ensure accessibility to mountain trails or natural parks, analysing the state of the art of the solutions available for people who use wheelchairs or other mobility aids. The definition of “persons with disabilities” adopted in this article follows that of the United Nations Convention on the Rights of Persons with Disabilities, which describes them as those who have long-term physical, mental, intellectual or sensory impairments which in interaction with various barriers may hinder their full and effective participation in society on an equal basis with others [10]. However, the analysis focuses exclusively on PwDs that affect their motor function, i.e., people with motor impairments who use autonomous aids such as classic self-propelled wheelchairs or aids that require assistance such as single-wheel wheelchairs [11,12,13].

The accessibility of natural areas and trails for people with motor disabilities presents numerous critical issues. A first significant problem is represented by physical barriers: unsuitable paths, uneven surfaces, excessive slopes, and inadequate infrastructures render the use of many natural spaces difficult, if not impossible. In particular, trails are often not designed to accommodate wheelchairs or mobility aids, actually excluding visitors with disabilities [7,9,14,15,16]. The lack of information and adequate signage is a further problem: clear data on accessible routes or their level of difficulty are rarely available, thus preventing the informed planning of trips [17,18,19]. The difficulty of the trails is assessed by considering objective parameters, such as the slope, the length of the sections and the surface of the ground [20,21,22].

Starting from these considerations, in the present article we address the issue of the classification of nature trails for PwDs who use self-propelled wheelchair and other mobility aids. In the context of the accessibility of nature trails for people with motor disabilities, it is essential to consider a diversified set of aids. In addition to self-propelled wheelchairs, there are technological devices such as auxiliary drives (power attachments) that improve autonomy on difficult terrain. Additionally, to ensure assisted mobility, there are single-wheel wheelchairs specifically designed for hiking, such as the well-known Joëlette [23]. These innovative aids help make the outdoor experience inclusive, allowing a wider audience to enjoy nature.

Another crucial aspect concerns the training of tourism service providers, who are not always prepared to understand and respond to the specific needs of tourists with disabilities. The lack of specific training can compromise the tourist experience, making it less inclusive [16]. In this context, universal design stands as a fundamental solution, as it allows for creating accessible environments for people regardless of their physical abilities, but unfortunately it is still rare in nature-based tourism [24]. Furthermore, the direct involvement of PwDs in the design of trails and infrastructure is essential to ensure that their needs are actually considered [25]. Unfortunately, this participatory approach is still not widespread, thus opening the risk that the design of new trails may not fully respond to the accessibility needs.

Finally, the paper reviews the existing guidelines for accessibility to trails and outdoor activities drawn up by national and international bodies [20,21,26,27,28]. These guidelines, although useful, are often fragmentary and lack a unified and integrated approach. Therefore, there is the need to develop more complete and homogeneous standards to ensure that all people with motor disabilities can enjoy an inclusive and safe experience on nature trails [26].

The review of the state of the art on accessible hiking, provided in this work, mainly aims to stimulate further research about the definition of a comprehensive definition of difficulty levels for accessible hiking trails. Consequently, to animate the debate on the need for more awareness and innovation, with the goal of making nature truly accessible to everyone.

2. Materials and Methods

The present review aims to identify some relevant themes within the academic literature, focusing on the scientific literature about accessibility in relation to nature-based tourism and outdoor activities.

2.1. Formulation of Research Questions

The main decision in preparing a review is to define its focus. This task is performed most effectively by asking clearly worded questions. Denyer et al. [29] defined this goal with the acronym CIMO (Context, Intervention, Mechanism, and Outcome). The acronym specifies the four critical parts of a well-structured question for a systematic review:

• Context (where?)
• Intervention (what?)
• Mechanism (how?)
• Result (to achieve what?)

In the case of our topic, it is possible to formulate the following research questions:

• How to design (M) interventions on paths and trails (I) in nature (C) to make them accessible to people with motor impairments (O)?
• What conditions (I) can improve the accessibility (O) of outdoor trails (C) for people with motor disabilities?

Once the research topic is clearly defined, an accurate list of keywords is developed. Keywords are defined through preliminary knowledge of literature terminology. For each element of the CIMO structure, the keywords are divided into subcategories, as shown in

Table 1. Keywords categorised by the CIMO framework to guide the literature search.

Context	Intervention	Mechanism	Outcome
Where? In which context the intervention is conducted	What? What is the main topic	How? What are the means	To get what? What is the wanted information
Nature	Interventions on routes/paths	Design	Accessibility for people with motor disabilities
Mountain	Tread Obstacles	Universal Design	Access
Park	Route Surfaces	Inclusive Design	Accessible
Forest	Gates and Barriers	Health Design	Accessibility
Wood	Slope	Design for all	Adaptive
Path	Wheelchair	Interventions	Disability
Route	Aid	Planning	Motor disability
Trail	Mobility aids	Barrier-free	People with Motor Impairments
Trekking	Support	Guidelines	People with physical disabilities
Hiking		Design
Outdoor		Universal Design
Open space		Inclusive Design

.

Subsequently, we conducted a systematic search on the Scopus database. To ensure the best relevance to our focus, the search was based on a combination of the most important keywords from the four categories of the CIMO framework. Terms belonging to the same category were combined with “OR”, while terms belonging to different categories were combined with “AND”:

• access* (access, accessible, accessibility)
• AND nature* OR outdoor OR park*
• AND wheelchair* OR “mobility aid*”
• AND disable* OR disability* OR impairment*

This search yielded an initial sample of 173 records, including journal articles, book chapters, research notes, and conference proceedings. The publications were subsequently screened to identify those fit for the literature review, i.e., accessibility in relation to nature-based tourism and outdoor recreational activities.

2.2. Application of Inclusion and Exclusion Criteria

We limited our search to the last twenty years, as research in this field before 2004 was still modest, and we focused only on publications in English. The application of these criteria reduced the initial sample to 135 documents. Titles and abstracts of results were screened for eligibility. Inclusion and exclusion criteria were applied to each article and study to determine whether the article was relevant to the review or not. Studies whose themes were potentially related to our objectives were selected based on the criteria described below:

• Context: Different natural sites such as parks, urban forests, outdoor recreation sites, and trails, where natural elements are more prevalent than man-made ones. Studies where outdoor environments are more man-made than natural, such as roads and sidewalks, were excluded.
• Participants: Individuals of all ages with motor disabilities were identified as our target group. Motor disabilities are very common among the elderly and in families with young children. Therefore, studies whose target groups were elderly or were focused on motor disabilities and parents with children in strollers were also considered eligible. The decision to include studies on other target groups and other levels of disability was based on the content of the study.
• Accessibility issues: We took into consideration only those accessibility issues related to outdoor activities that led to a better use of trails and outdoor recreation areas with scientific and reasonable solutions. Barriers found in enclosed spaces, man-made roads, and transportation infrastructures were not included in our scope.

Following the screening of titles and abstracts, we reduced the corpus to 10 documents that fully aligned with the objectives of the study.

2.3. Documents Found Through Other Searches

To broaden the analytical perspective, we conducted supplementary searches using Google, along with a citation analysis of the 10 selected articles. This process led us to the identification of an additional 26 documents not indexed in Scopus. Results of the application of the methodology can be summarized as in Figure 1. These include reports, guidelines and documents produced by national and international associations, government agencies and organisations, with the aim of integrating academic literature with data and operational approaches from both public and private sources. A graphical summary of the main themes identified is available in Figure 2.

From the analysis of these materials, we identified four main areas of intervention:

• Aids for accessing the routes (independently and with assistance).
• Trail classifications for PwDs.
• Trail accessibility guidelines.
• Local complementary services.

In particular, we also conducted a literature search and a market analysis of the different technical solutions for the movement of PwDs on rough terrain in order to obtain an overview of the wheelchair aids and accessories. Another document search was conducted to trace the different classifications of routes for PwDs that consider all the aids available on the market, according to objective evaluation criteria such as gradient, surface of the path and length of the sloping sections. The last sections present several national and international guidelines that offer customised and practical solutions to improve the accessibility of nature trails, together with studies on inclusive design that directly involves PwDs and on the need for better training of tourism service providers. To summarise the information of each document, we created

Table 2. Characteristics of included studies.

Authors (Country)	Title (Document Type)	Problem Statement— Purpose	Methodological Philosophy	Research Methods— Specifics	Findings— Results	Unsolved Problems
Agovino M.; Casaccia M.; Garofalo A.; Marchesano K. 2017 (Italy) [18]	Tourism and disability in Italy. Limits and opportunities (Article)	Tourism demand of PwDs. Factors that hinder or encourage participation	Qualitative	Secondary data from Italian sources	Significant tourism segment with growing demand	Many limitations hinder the development of accessible offering
Aziz, N.; Khusaini, N.S.; Mohamed, Z.; Hamid, A.; Yusof, Y.; Aziz, M.R. 2022 (Malaysia) [30]	Smart Wheelchairs: A Review on Control Methods (Conference paper)	Examines smart wheelchair control methods, emphasising advancements in AI, sensors, and user interfaces	Qualitative	Literature Review	Advancements in smart wheelchair control methods, focusing on AI, robotics, and sensor integration	Limited autonomous navigation, sensor reliability, cost and accessibility
Baronio, G.; Bodini, I.; Motyl, B.; Uberti, S. 2021 (Italy) [12]	Prototyping, Testing, and Redesign of a Three-Wheel Trekking Wheelchair for Accessible Tourism Applications (Article)	Validating by testing the prototype of a trekking wheelchair for PwDs	Qualitative	Data on stability, effort required for handling, and safety	Drivability problems under some conditions and contribution of design changes	New model optimisation with quantitative testing to assess comfort, handling and energy consumption
Baronio, G.; Bodini, I.; Motyl, B.; Uberti, S. 2017 (Italy) [11]	Gölem project: Concept and design of a trekking/hiking wheelchair (Article)	Design and test an improved model of a hiking wheelchair	Mixed	Experimental tests on performance, such as stability, material strength, and handling	Improvement over commercially available aids in comfortand functionality	Improving handling in extreme terrain, and customization for users with different needs
Benjamin, S., Bottone, E., & Lee, M. 2020 (USA) [31]	Beyond accessibility: exploring the representation of people with disabilities in tourism promotional materials (Article)	How are represented PWDs in promotional materials, particularly in brochures tourism	Qualitative	Content analysis of 211 tourism brochures, from nine southeastern U.S. states	Images and text referring to PwDs rarely appear in promotional materials	Broaden the context of analysis and directly involve tourism stakeholders
Bianchi, P.; Cappelletti, G.M.; Mafrolla, E.; Sica, E.; Sisto, R. 2020 (Italy) [14]	Accessible Tourism in Natural Park Areas: A Social Network Analysis to Discard Barriers and Provide Information for People with Disabilities (Article)	How accessibility information is shared among stakeholders in the Gargano Park (southern Italy) and how it can be improved to foster inclusive tourism	Quantitative	Social Network Analysis (SNA), focuses on relationships and information flows among stakeholders using mathematical and statistical tools	The information flow is dominated by a single government administration, while some nodes remain passive	Involve users in decisions and foster more effective exchange of information among stakeholders
Blaszczyk M.; Suchocka M.; Wojnowska-Heciak M.; Muszynska M. 2020 (Poland) [5]	Quality of urban parks in the perception of city residents with mobility difficulties (Article)	Availability and accessibility of parks	Qualitative	Questionnaire, survey	Typical activities of people with limited mobility and most dominant barriers	Recommendations and guidelines for accessibility of disabled people in parks
Chikuta, O.; du Plessis, E.; & Saayman, M. 2018 (South Africa) [32]	Accessibility Expectations of Tourists with Disabilities in National Parks (Article)	Expectations and needs of PwDs regarding accessibility of national parks	Mixed	Online questionnaire with demographic and accessibility expectations data	Strong desire for autonomy of PwDs. Universal design of natural spaces	Representativeness of the sample
Cloquet, I.; Palomino, M.; Shaw, G.; Stephen, G.: & Taylor, T. 2017 (UK) [33]	Disability, social inclusion and the marketing of tourist attractions (Article)	How tourist attractions in Cornwall (England) address the inclusion of PwDs through marketing and communication strategies	Mixed	Analysis of brochures and websites	Poorly considered accessibility information in both text and images	Does not integrate PwDs’ views and does not propose concrete operational solutions
Club Alpino Italiano 2021 (Italy) [34]	Classificazione dei percorsi montani accessibili con ausili (Manual)	Classification of difficulty of accessible routes with aids for people with motor disabilities	-	It is not a scientific study. It is based on criteria developed by the Italian Alpine Club in collaboration with other bodies	Three route classes with specific technical require-ments	Not all possible aids for people with motor disabilities are considered
Corazon, S. S.; Gramkov, M. C.; Poulsen, D. V.; Lygum, V. L.; Zhang, G.; & Stigsdotter, U. K. 2019 (Denmark) [15]	I Would Really like to Visit the Forest, but it is Just Too Difficult: A Qualitative Study on Mobility Disability and Green Spaces (Article)	Experiences and related constraints of individuals with mobility disabilities visiting green space	Qualitative	Group and individual interviews	Structural problems of trails and lack of accessibility information on websites	Practical solutions that could facilitate access to trails
Darcy, S.; Cameron, B.; & Pegg, S. 2010 (Australia) [35]	Accessible tourism and sustainability: a discussion and case study (Article)	Exploring the interrelationship between accessible tourism and sustainability	Qualitative	Analysis of secondary sources, such as planning documents, guidelines, institutional reports, and technical publications	Accessibility is fully compatible with the three pillars of sustainability: environmental, social, economic	Limitations related to absence of empirical data, lack of generalizability of the case, and lack of evaluative tools
Eusébio, C., Alves, J. P., Carneiro, M. J., & Teixeira, L. 2024 (Portugal) [4]	Needs, motivations, constraints and benefits of people with disabilities participating in tourism activities: the view of formal caregivers (Article)	Exploring formal caregivers’ perceptions of the needs, motivations, constraints, and benefits of tourism for PwDS	Qualitative	Semi-structured interviews with formal caregivers	Several strategic recommendations: improve accessibility, train staff, and provide clear information	Operational indications not translated concretely into effective and sustainable policies or projects over time
Fialová J.; Kotásková P.; Schneider J.; Žmolíková N.; Procházková P. 2018 (Czech Republic) [19]	Geo-caching for wheelchair users: a pilot study in luhacovské zálesí (czech republic) (Article)	Evaluate the accessibility of geocaching activities for wheelchair users	Mixed	Numerical data regarding the physical characteristics of the trails. User feedback	Rules for establishing caches suitable for wheelchair users	Rules accepted by at least some of the gaming community
Fieldfare Trust Ltd. 2005 (UK) [26]	Countryside for All. Good Practice Guide: A Guide to Disabled People’s Access in the Countryside (Technical Manual)	Practical guidelines for improving the accessibility of natural environments to PwDs by promoting an inclusive approach in design	-	It is not a scientific study, but an operational guide. It is based on field experiences, best practices and current regulations	Disseminate inclusive standards for accessibility in rural settings, influencing public agencies and trail managers	It does not solve the difficulties of application in complex natural settings. The absence of updates for years has made some directions outdated
Garrod, B.; & Fennell, D. A. 2021 (UK) [36]	Strategic approaches to accessible ecotourism: small steps, the domino effect and not paving paradise (Article)	Exploring strategic approaches to make hiking accessible to PwDs, without compromising the environmental integrity of natural places	Qualitative	Interviews with accessible ecotourism providers and consultants from different countries	Three strategies: small steps incremental, the domino effect of barriers, and an approach for environmental conservation	Conflict between goals of accessibility and preservation
Godtman Kling, K. & Ioannides, D. 2022 (Sweden) [16]	Enhancing Accessibility in Tourism and Outdoor Recreation: A Review of Major Research Themes and a Glance at Best Practice (Technical Report)	Analyse major research topics on accessibility in tourism and outdoor recreation, highlighting existing good practices	Qualitative	Narrative literature review, collection and qualitative analysis of case studies and best practices	Identifies five macro-themes and reports good practices based on inclusive design and participation	Fragmentary studies and lack of internationally comparable data
Groulx, M., Lemieux, C., Freeman, S., Cameron, J., Wright, P. A., & Healy, T. 2021 (Canada) [25]	Participatory planning for the future of accessible nature (Article)	How participatory processes can improve the design of accessible natural spaces by involving PwDs and other stakeholders	Qualitative	Workshops, interviews and moments of collective discussion	Best practices for inclusive design and development of practical guidelines for actively engaging PwDs	Lack of resources to implement solutions, difficulty in involving all stakeholder groups, bureaucratic barriers
Irish Wheelchair Association; Sport Ireland 2018 (Ireland) [28]	Great Outdoors—A guide for accessibility (Technical Manual)	Making natural spaces in Ireland accessible to all, including PwDs	-	Participatory methodology, involving PwDs and stakeholders through consultations and self-assessments	Inclusive design of trails and parks according to Universal Design	Difficulties in rugged natural terrain and the need for more training among operators
Leaman, J.; La, H.M. 2017 (USA) [37]	A Comprehensive Review of Smart Wheelchairs: Past, Present, and Future (Review)	Aims to provide a systematic review of Smart Wheelchair	Mixed	Systematic literature review	Main research trends, such as autonomy, intelligent navigation, and human–machine interaction	Limited autonomous navigation, unintuitive user interfaces, sensor reliability, high cost.
Lepoglavec K.; Papeš O.; Lovrić V.; Raspudić A.; Nevečerel H. 2023 (Croatia) [22]	Accessibility of urban forests and parks for people with disabilities in wheelchairs, considering the surface and longitudinal slope of the trails (Article)	Accessibility of urban forests and parks for people with disabilities in wheelchairs	Quantitative	Test of measurement of the mobility of people in wheelchairs	Classification of paths based on slope	Consider different surfaces for slope categorization and park management guidelines
Janeczko, E.; Jakubisová, M.; Woźnicka, M.; Fialova, J. & Kotásková, P. 2016 (Poland; Slovak Republic; Czech Republic) [9]	Preferences of people with disabilities on wheelchairs in relation to forest trails for recreational in selected European countries (Article)	Analyse the preferences of wheelchair users regarding recreational forest trails in some European countries	Quantitative	Collection and analysis of data through questionnaires to people with mobility disabilities who use wheelchairs	Surface and slope of trails, along with the presence of accessible facilities, are crucial elements	Does not conduct a direct survey of pathways with PwDs
Lundell, Y. 2005 (Sweden) [20]	Access to the Forests for Disabled People (Technical Manual)	Guidelines on accessibility of forest areas for PwDs, focusing mainly on those with mobility or visual impairments	-	It is not a scientific study, but an operational guide. It is based on field experiences and best practices	Improving the accessibility of Sweden’s forests by providing guidelines and raising awareness among forest managers	Structural, economic, and cultural constraints to a full accessibility of forests
McCabe, S., & Diekmann, A. 2015 (UK; Belgium) [2]	The rights to tourism: reflections on social tourism and human rights (Article)	Analyse whether tourism can be recognised as a social right and reflect on its role in inclusion through social tourism	-	Conceptual and argumentative approach	Reconsidering tourism as a social right, recognising its potential to promote justice and inclusion	Operational, legal and empirical issues concerning the effective implementation of the ‘right to tourism’
Moura, A. F. A., Kastenholz, E., & Pereira, A. M. S. 2017 (Portugal) [3]	Accessible tourism and its benefits for coping with stress	Exploring whether and how accessible tourism can contribute to stress management in PwDs	Quantitative	Leisure Coping Scale, specifically adapted to the context of accessible tourism. Sample of 306 PwDs	The value of tourism as a coping resource and suggest its integration into policies and therapeutic practices	Limitations in the generalizability of the results. It does not explore structural barriers to access and lacks a comparison with people without disabilities.
National Confederation of Disabled People of Greece 2019 (Greece) [27]	Guidebook for Accessible Nature Trails: Design Guidelines and Evaluation System	Guidelines and an evaluation system for designing accessible nature trails, especially for people with mobility disabilities	-	Literature review, participatory design approach and practical field observations	Practical guidelines for accessible trail design and evaluation system for accessibility of existing trails	Lack of uniformity due to the variability of nature trails, and the difficulty of maintaining accessible trails over time
Poldma T.; Carbonneau H.; Miaux S.; Mazer B.; Le Dorze G.; Gilbert A.; Hammouni Z.; El-Khatib A. 2017 (Canada) [17]	Lived experiences and technology in the design of urban nature parks for accessibility (Conference paper)	Mobility challenges in urban parks for people with wheelchair disabilities	Qualitative	User conversations and observations in real time	Navigation technologies such as mobility apps improve access to parks	Physical barriers and poor information and way-finding
Rowiński, R.; Morgulec-Adamowicz, N.; Ogonowska-Slodownik, A.; Dąbrowski, A.; Geigle, PR. 2017 (Poland; USA) [8]	Participation in leisure activities and tourism among older people with and without disabilities in Poland (Article)	To compare physical activity and participation in recreational and tourist activities among older people with and without disabilities in Poland	Quantitative	Analysis of data from a large-scale survey targeting 3743 elderly people in Poland	PwDs are less active in tourism and physical activities	The needs of PwDs in relation to recreation and tourism activities are not addressed
Shen, Xj.; Huang, Rh. & Zhang, Js. 2019 (China; Usa) [7]	U.S. national parks accessibility and visitation (Article)	Analyses the accessibility of U.S. parks, examining physical barriers and proposing solutions for PwDs	Quantitative	Analysis of the correlation between visitation and accessibility, according to park types	Accessibility for PwDs influences the number of visits to national parks variably	Causes of correlations between accessibility and attendance are not explored in depth
Singh, R., Sibi, P. S., Yost, E., & Mann, D. S. 2021 (India; USA) [1]	Tourism and disability: a bibliometric review (Review)	Analyse research on tourism and disability, mapping trends, relationships, and emerging themes in the field	Quantitative	Bibliometric analysis	Growth in research on tourism and disability. Key topics: assistive technology, sustainable tourism and dedicated marketing	Limited geographical coverage. Little integration between theoretical and practical approaches.
Sreevatsav, S.; Sheth, S.; Kumar, A.; Dwivedy, B. 2023 (India) [13]	An iot enabled smart wheelchair solution for physically challenged people (Conference paper)	IoT smart wheelchair enhances mobility, autonomy, and safety	Quantitative	Design and development of the prototype	Enhancement of a traditional wheelchair’s functionalities.	Reliability in real-world conditions. Cost
Sukerkar, K.; Suratwala, D.; Saravade, A.; Patil, J.; D’britto, R. 2018 (India) [38]	Smart Wheelchair: A Literature Review (Review)	Aims to analyse the current state of smart wheelchair technology	Qualitative	Literature review	Technological advances in smart wheelchairs, integrating AI, robotics and sensors	Challenges such as high cost, accessibility and reliability
Svizzera Mobile (Switzerland) [39]	Obstacle-Free Routes, Grade of Difficulty (Manual)	Provide difficulty levels for trails for PwDs	-	It is not a scientific study, but an operational guide. It is based on criteria developed by various organisations and PwDs	Three route classes with specific technical requirements	Not all possible aids for people with motor disabilities are considered
Wall-Reinius, S.; Kling, K. G.; & Ioannides, D. 2022 (Sweden) [24]	Access to Nature for Persons with Disabilities: Perspectives and Practices of Swedish Tourism Providers (Article)	Challenges and opportunities of tourism service providers in Sweden in providing access to nature for PwDs	Qualitative	Semi-structured interviews conducted with tourism service providers	Positive examples of inclusive practices and readiness for change emerge, if supported by appropriate training and policies	Accessibility to nature for PwDs is still not a priority for many tour operators, due to cultural, economic and regulatory barriers
Zeller, J.; Doyle, R.; Snodgrass, K. 2012 (USA) [21]	Accessibility Guidebook for Outdoor Recreation and Trails (Technical manual)	Provide technical and operational guidelines for making outdoor recreation and trails accessible to PwDs	-	Analysis of existing standards, experiences practices, and accessibility guidelines	Technical reference tool and regulatory tool to ensure equal access to nature	Adaptability to specific contexts, cost of implementation, long-term maintenance. Does not include different disabilities
Zhang, G.; Poulsen, D.V.; Lygum, V.L.; Corazon, S.S.; Gramkow, M.C.; Stigsdotter, U.K. 2017 (Denmark) [6]	Health-Promoting Nature Access for People with Mobility Impairments: A Systematic Review (Review)	Systematically evaluate scientific evidence for health benefits of natural environments for people with mobility impairments	Mixed	Systematic literature review	Access to nature brings physical, mental and social benefits to people with developmental disabilities	Persistence of numerous environmental and social barriers

.

Despite the geographical variety of the studies, the literature on the subject still appears fragmented, with limited research using objective criteria and field tests for the classification of accessible paths. Such approaches, although rare, represent an important innovation, as they allow for a concrete assessment of the difficulties encountered by people with motor disabilities in relation to the aids they use. Further exploration of these aspects is essential to provide useful tools for designers and policy makers. In this context, the study proposes an integrated synthesis of existing classifications.

3. Results

The analysis of the materials presented in Section 2 has allowed us to identify two main thematic areas: on the one hand, the aids that facilitate access and use of nature trails by PwDs; on the other, the classification systems of accessible trails, which are essential for providing clear, reliable, and comparable information on the actual practicability of the itineraries. In particular, in Section 3.1, we focus on the aids for independent use, i.e., devices that allow people with motor disabilities to move independently on the trails, while in Section 3.2, we examine the aids that require the assistance of able-bodied companions. In Section 3.3, we present a comparative analysis of the main classification systems for accessible trails, examining the methodologies adopted at both national and international levels. Subsequently, in Section 3.4 we propose a critical synthesis of the models analysed, with the aim of outlining a more integrated and functional classification of difficulty levels.

Finally, in Section 3.5 and Section 3.6, respectively, we examine some operational guidelines for improving accessibility in natural contexts and studies on inclusive design, with particular attention to the direct involvement of PwDs and integration with complementary services in the area.

3.1. Aids to Be Used Independently

There are several tools that allow people with motor disabilities to access nature trails. The most common is the self-propelled wheelchair, a mobility aid that the user can move independently with by using his/her arms to push the rear wheels. This type of wheelchair offers a certain degree of independence for people with motor disabilities, allowing them to move autonomously on tracks and slight slopes.

Self-propelled wheelchairs are divided into different types, depending on the structure and the user’s needs. The main categories are

• Rigid frame wheelchair: characterised by a fixed and non-folding frame, which guarantees greater rigidity and stability. This model is generally lighter, which makes it easier to use for people who have good self-propulsion abilities. Ease of handling and movement are two of its main advantages.
• Folding wheelchair: equipped with a mechanism that allows the frame to be folded, making it easier to transport and store. However, compared to rigid-frame wheelchairs, these wheelchairs tend to be heavier and may be slightly less responsive in movement due to the greater flexibility of the frame.

To better move on rough terrain, there are accessories for self-propelled wheelchairs such as the small wheel (FreeWheel [40]; Offcar, EasyWheel [41]) and mountain bike wheels. Furthermore, it is possible to motorize a self-propelled wheelchair thanks to devices such as front motors (Batec [42], Klaxon [43], Triride [44]) and rear drives (Triride, Trekking Power [45]). These devices attach easily to the wheelchair, offering PwDs a greater autonomy even on more difficult routes. There are also single-wheel wheelchairs for use with the assistance of non-disabled assistants: the best known is the Joëlette [23], the first to be patented with this system, which we will discuss later.

3.1.1. Small Wheel for Wheelchairs

The small wheel is an additional wheel that is applied to the front frame of classic self-propelled wheelchairs, as in Figure 3. Designed for rigid wheelchairs, it can also be used on folding wheelchairs through an adapter, transforming classic four-wheeled wheelchairs into a three-wheeled aid. By raising the front wheels of the wheelchair, this support allows for a greater freedom of movement and less effort on uneven or dirt tracks. Likewise, the assistant who pushes the wheelchair receives some help as well. By using this accessory, the user avoids having to “wheelie” the wheelchair on these types of surfaces and is helped in overcoming obstacles, such as steps and pavements in urban environments, or stones and roots in nature.

3.1.2. Off-Road Wheels

Off-road wheels can be fitted to replace the standard wheels on self-propelled wheelchairs. A sturdy wheel, suitable for dirt surfaces, may be mounted on wheelchairs. These wheels have a tyre with a wide section and a knobby profile, of the same shape as mountain bike wheels. These wheels maintain the same diameter as a road wheel (24″) but compared to the latter, they have a greater thickness: a variable width between 1.75″ and 2.15″ for off-road wheels compared with 1″ of ordinary road wheels. This type of tread has a knobbly profile that increases traction and improves wheel comfort; therefore, it is recommended for wheelchairs equipped with auxiliary drives as described below.

3.1.3. Auxiliary Drives

The auxiliary drive, also called power attachment, is an electric small wheel with a handlebar that is attached to the front frame of a self-propelled wheelchair.

Equipping a self-propelled wheelchair with this type of device significantly increases the autonomy of PwDs, even on challenging routes, with uneven terrain and significant slopes. Instead of acting on the wheelchair’s push-rims, the disabled person can benefit from an auxiliary drive that transforms the wheelchair into a real scooter, equipped with handlebar. The various anchoring systems of the motors available on the market, by lifting the front wheels of the wheelchair, convert the classic four-wheeled wheelchairs into a three-wheeled motorised aid. When no longer needed, the motor can be removed, so that the wheelchair returns to its original shape more fit for narrow or domestic spaces.

There are several models on the market, produced by various specialist companies (Batec [42], Klaxon [43], Triride [44]), such as those depicted in Figure 4.

The models differ on some technical specifications of the motors and the geometries of the frame and wheels (

Table 3. Technical specifications of auxiliary drives produced by major companies.

Model	Voltage Battery	Power Motor	Diam./Width Tyre	Weight 1	Range 2
TRIRIDE [44]
Kids	36 V	540 W	12″	7.5 kg	35 km
Folding	36 V	670 W	12″	8.2 kg	35 km
Light	36 V/48 V	670 W/890 W	12″/14″	8.5 kg	50 km
Light 10″	36 V/48 V	670 W/890 W	10″	7.8 kg	50 km
Special Light	36 V/48 V	900 W/1200 W	12″/14″	8.5 kg	50 km
Special Compact HT	36 V/48 V	1000 W/1400 W	12″	11 kg	50 km
Special L14	48 V	1500 W	14″	11.9 kg	50 km
Special HP16	48 V	1500 W	16″	12.8 kg	50 km
Mad Max	48 V	1500 W	16″	12.8 kg	50 km
T-Rocks	48 V	1500 W	16 × 4	12.8 kg	50 km
KLAXON MOBILITY [43]
Klick Power	48 V	750 W	14″	8.5 kg	50 km
Klick Race	48 V	1500 W	14″	11.4 kg	50 km
Klick Monster	48 V	1500 W	20″	15 kg	50 km
BATEC MOBILITY [42]
Batec Mini 2	36 V	350 W	12 × 2.40	12.9 kg	52 km
Batec Electric 2	36 V	900 W	18 × 2.40	15.9 kg	35 km
Batec Rapid 2	36 V/48 V	1440 W	18 × 2.40	15.9 kg	50 km
Batec Scrambler 2	36 V/48 V	1440 W	19 × 2.75	16.7 kg	50 km

¹ The weight refers to the device excluding the battery and wheelchair support arms. ² Range refers to use on a flat path at an average speed of 6 km/h (level 1) with a user weight of 70 kg. The actual range depends on the user’s weight, the condition of the wheelchair and tyres, the road conditions, the type and condition of the battery, the speed, and the driving style.

):

• Voltage, unique parameter for battery and motor, measured in Volts [V].
• Power, speed at which a motor can make a movement, measured in Watts [W].
• Torque, rotational force that an engine can impart, measured in Newton-metre [Nm].
• Tyre diameter and width, measured in Inches [″].

Devices with low engine power and small wheels are ideal for urban mobility; those with high power and large wheels are more efficient for moving around nature on dirt surfaces. A compromise for city trips and day trips are those with intermediate power and tyre diameter values.

In the case of models for hikes on dirt surfaces, to achieve a good traction, the devices are already equipped with wide-section and knobby tyres. When combining a traction device with a classic self-propelled wheelchair, it is also necessary to replace the two standard rear wheels with off-road wheels, such as mountain bike wheels, as seen in the previous paragraph.

The standard features of these devices include 5 selectable power levels, reverse gear, and disc brake. Furthermore, the latest generation models feature:

• IBS—Intelligent Braking System: Fully electronic braking system, with programmable and customizable intensity. Anti-slip system and battery charging during braking.
• ICC—Intelligent Cruise Control: In addition to the normal Cruise Control function, it allows for maintaining the set speed even when going downhill, adapting to changes in slope, without requiring the use of the brake.
• MDC—Motion Direct Control: Electronic traction control system (speed control). With just one command (accelerator) the user has a total control over the movement of the device and its pace.
• Eco Drive System: It acts on the delivery of the maximum power of the device with five programmable and customizable levels.

Auxiliary drives are customizable and adaptable for users with tetraplegia or other types of limited upper limb mobility. In this case, the devices are tailor-made according to the user’s needs, to always guarantee an optimal and safe driving through a peculiar handlebar configuration, combined with other features and accessories.

Among the potentially critical aspects of an auxiliary drive, there is the slipping of the motorised wheel when used on steep slopes and on dirt terrain. The front wheel slipping, in these cases, is due to the unbalanced load on the rear wheels of the wheelchair. Obviously, much depends on the driving ability of the user who, to avoid this inconvenience, will have to move the torso a little forward and modulate the acceleration. To overcome this problem, a rear drive kit for wheelchairs was designed, described in the following paragraph.

3.1.4. Rear Drive Kit for Wheelchairs

This device allows for transforming a classic wheelchair into an electronic wheelchair by simply replacing the standard wheels with motorised ones (Triride, Trekking Power [45]). The kit is compatible and can be installed on most wheelchairs on the market, both with rigid and folding frames, and can be easily removed, returning the wheelchair to its original state without any structural modifications. The motorised wheels provide rear-wheel drive that allows for tackling dirt paths and very difficult climbs. Furthermore, when combined with a front auxiliary drive, a classic wheelchair is transformed into a 3-wheel drive aid to tackle even very challenging routes without the inconvenience of the front wheel slipping.

3.2. Aids to Be Used with Assistance

In addition to the aids seen in the previous paragraphs for classic self-propelled wheelchairs that help to move independently on uneven terrain, there are others that need to be used by non-disabled assistants.

3.2.1. Joëlette

The Joëlette [23] is the most popular single-wheeled wheelchair that allows persons with reduced mobility to go hiking with the help of able-bodied assistants. It owes its name to its inventor, a Frenchman named Joël Claudel, who conceived and built it to be able to take his nephew, who suffered from a neuromuscular disease, up to the mountains. In addition to the classic version, the same company produces a model with electrical auxiliary drive [46]. Other companies make similar aids on a single wheel (TrailRider [47]) and also on two closely spaced wheels such as the K-bike (Offcar, K-bike [48]), as in Figure 5.

Hiking with a Joëlette is an important choice for a person with disabilities, as it involves giving up the autonomy of the self-propelled wheelchair, to rely completely on assistants for their mobility and safety.

The Joëlette is a wheelchair with the seat installed on a frame placed in a central position on a single fat-bike wheel, equipped with a disc brake and a shock absorber to dampen vibrations. At the front of the frame, two curved arms allow the wheelchair to be gripped and pulled by an assistant. At the rear there is a handlebar, controlled by the second assistant, with the disc brake control.

As specified in the user manual [49], the number of assistants required to drive a Joëlette can vary from two to five people, depending on the difficulty of the route, the experience of the assistants, and the weight of the passengers. The standard crew of a Joëlette consists of one passenger and two assistants. With experience, if the route is not difficult and the passenger is light-weighted, it is possible to have only two assistants per wheelchair. Each assistant has a specific task depending on his/her position.

The front assistant pulls the Joëlette and is responsible for choosing the route and avoiding major obstacles. It plays the role of an “engine”, i.e., provides the traction energy to move the wheelchair forward. The rear assistant balances the Joëlette and is responsible for the correct positioning of the wheelchair and ensuring that it remains horizontal so that the passenger’s weight remains over the wheel at all times. On downhill sections, the assistant applies the brake to ensure a smooth advancement.

Any other Joëlette assistant has the task of replacing one of the assistants when he/she gets tired. They also help towing the Joëlette up steep hills by positioning themselves in front of the wheelchair and pulling with a strap attached to the inside of the front arm brackets. They can also assist in towing or crossing obstacles by positioning themselves on the sides at the passenger’s height and pulling the Joëlette along the armrests or side handles.

3.2.2. Emerging Technologies: Smart Wheelchairs and IoT Devices

In recent years, an important area of research and technological development has emerged around smart wheelchairs and mobility solutions based on the Internet of Things (IoT). Smart wheelchairs are equipped with a variety of sensors, control systems, and connectivity features that can support autonomous navigation, obstacle detection, and improved user interaction [30,37,38]. Despite these advances, their application in hiking or natural settings is still limited. Most of the technological implementations remain within indoor or urban contexts, with few examples being tested on rough or unstructured outdoor terrain. Therefore, while traditional aids such as the Joëlette remain dominant in hiking scenarios, smart wheelchairs and IoT devices represent an innovative frontier with significant potential for the future of accessible outdoor tourism.

3.3. Trail Classification for PwDs

The classification of accessible routes for PwDs is essential to provide clear and reliable information on the feasibility of the trails. Various studies, conducted by both public and private organisations, have developed classification systems based on objective criteria. They allowed for the identification of the most suitable routes according to the different levels of independence of the users. This approach promotes a greater inclusion and a better awareness in outdoor activities, making the hiking experience more accessible.

Starting from such a consideration, the following Section 3.3.1, Section 3.3.2 and Section 3.3.3 analyse the studies related to the classification of trails difficulty. We conducted the analysis by grouping the discussed studies according to the specific mobility aid that they consider for the classification. In the next Section 3.4, we present the synthesis of all the studies analysed in section to propose a novel and comprehensive definition of hiking trails difficulty levels based on specific characteristics (slope, surface, etc.) and present the suitable mobility aids for each level.

3.3.1. Trail Classification for Self-Propelled Wheelchair

Several authors have classified trails for PwDs who use a self-propelled wheelchair, also specifying whether these itineraries can be tackled independently or with the help of an assistant. The different difficulty scales have been drawn up, taking into consideration various objective parameters of the paths: the type of terrain surface, the maximum slope, the maximum length of the slope sections between one flat section and the next (resting spots) and the overall length of the trail.

The classification of the difficulty of the trails is the starting point to provide the most accurate information to those who want to venture on a path or an activity in the mountains and want to do it in an informed way.

Lundell (2005) [20] developed the first classification that introduced specific parameters on the slope of paths accessible to PwDs in Sweden. This study was published in a manual prepared for the National Board of Forestry in Sweden, with the aim of providing guidelines for the adaptation of forest paths and improving their accessibility for PwDs. According to the study, slopes steeper than 5% should be avoided. On such slopes, many wheelchair users can still get by without assistance. On slopes steeper than 5%, the trail should be designed with resting spots on flat surfaces every 5 metres. In areas considered accessible to PwDs, steep slopes may be accepted only in special circumstances and over very short distances.

Summarising the results of Lundell, we can define these three classes of paths:

• easy: slopes ≤ 5%, mobility with little or no assistance required;
• moderate: slopes > 5% (with resting spots every 5 m), mobility may require assistance;
• most difficult: slopes ≥ 5%, mobility will require assistance.

In the United States, Zeller et al. (2012) [21] address the issue of classifying trails for people with disabilities, within the Accessibility Guidebook for Outdoor Recreation and Trails, to be applied on National Forest System lands. According to this study, nature trails of any length can have a maximum gradient of 5% for autonomous crossing in a self-propelled wheelchair. A steeper terrain can be difficult to access, although many people can handle greater slopes for short distances. To maintain accessibility for gradients greater than 5%, relatively flat areas can be used for resting before continuing along the route. These pauses are required every 61 metres for slopes of 5–8.33%, every 9 metres for slopes of 8.33–10% and every 3.05 metres for slopes of 10–12%. A route may never exceed a 12% gradient; beyond this limit, assistance is mandatory.

Summarising the results of Zeller et al., we can define these four path classes:

• easy: slopes ≤5 %, mobility with little or no assistance required;
• moderate: gradients of 5–8.33%, mobility may require assistance;
• difficult: gradients of 8.33–10%, mobility may require assistance;
• most difficult: slopes ≥ 10%, mobility will require assistance.

Similar categories were mentioned in the most recent study, that of Lepoglavec et al. (2023) [22], which addresses the issue of accessibility of forests and urban parks in Croatia for PwDs in wheelchairs. Through tests conducted on six different trails and involving eight participants who moved independently using a self-propelled wheelchair, the trails were classified based on measurements obtained through spatial data analysis.

In this research, the selected paths had a macadam (dirt) surface without protrusions or holes that could cause problems for wheelchair users. It is a salient issue because these factors significantly impact on the accessibility of trails for PwDs.

The first stage was the survey of the routes, first by recording the tracks using the Gaia GPS mobile app, and subsequently via GNSS GPS instruments and a total (geodetic) station, obtaining precise longitudinal slope measurements. The limit slopes were defined through tests and field measurements. Then, they were evaluated by recording the heart rates of the subjects along the route and collecting the opinions of the interviewees themselves about the insecurity experienced.

The final result, obtained as a GIS map of the research area, indicates the sections of the routes that wheelchair users can cross independently, the areas that are accessed with a certain risk, and those that are not accessible. Each of them is referred to a specific interval of longitudinal slope.

According to this research, the maximum slope that allows an autonomous use of a self-propelled wheelchair is 5.50%; for these slope values, there is almost no sense of insecurity or risk for people in wheelchairs. A gradient of 9.01%, on the other hand, was determined as the maximum longitudinal gradient above which autonomous movement is not suitable for wheelchair users. It creates a very high feeling of insecurity in the event of forced movement along the path. At intermediate slopes, between 5.50 and 9.01%, subjects feel unsafe, and usability is very subjective, depending on physical fitness, health conditions and level of disability. In this last range of slopes, mobility may require assistance.

Summarising the results of the research by Lepoglavec et al., we can therefore define these three path classes:

• easy: slopes ≤ 5.50%, mobility with little or no assistance required;
• moderate: gradients of 5.5–9%, mobility may require assistance;
• most difficult: slopes ≥ 9.01%, mobility will require assistance.

Table 4. Definition of path difficulty classes for PwDs using self-propelled wheelchair according to three different studies.

		Lundell, Y. (2005) [20]		Zeller, J. (2012) [21]		Lepoglavec, K. (2023) [22]
Path Category	Assistance Required	Slope	Max. Length of Segment	Slope	Max. Length of Segment	Slope	Max. Length of Segment
easy	Little or no assistance required	≤5%	-	≤5%	-	≤5.5%	-
moderate	May require assistance	>5%	5 m	5–8.33%	61 m	5.51–9.01%	-
difficult	Assistance required	-	-	8.33–10%	9 m	-	-
most difficult	Assistance sorely required	≥5%	-	10–12%	3.05 m	>9.01%	-

compares the values of the slopes and lengths between the resting spots for the different difficulty categories proposed in the three aforementioned studies.

The slope values proposed in the three studies differ in their determination method. The study by Lepoglavec et al. [22] is the only one in which data are obtained with field tests, while those of Lundell [20] and Zeller et al. [21] are included in a manual and in guidelines, respectively, without details about the definition of parameters.

In addition, all the three difficulty scales focus exclusively on self-propelled wheelchairs, without considering other aids that could improve PwD’s independence or the level of accessibility of the routes.

3.3.2. Club Alpino Italiano—Classification of Accessible Mountain Routes

The Club Alpino Italiano (CAI) is the oldest and largest association of mountaineers and mountain enthusiasts in Italy [50,51].

Taking into account three fundamental objective parameters such as the difference in altitude, the planimetric distance and the signage of the route, the Club Alpino Italiano has adopted, at a national level, a scale to evaluate the trails with the following levels of difficulty [52]:

• T = Tourist. Paths that develop on small roads, mule tracks or comfortable trails, with altitude differences of less than 500 m. These hikes do not require particular experience or physical preparation.
• E = Hiker. Paths that almost always take place on trails with altitude differences between 500 and 1000 m. They require training in walking, as well as suitable footwear and equipment.
• EE = Experienced Hiker. Paths that require a good ability to move through impervious or steep terrain, with altitude differences normally greater than 1000 m. They require good hiking experience and good physical preparation, as well as adequate equipment and gear.
• EEA = Experienced Hiker with Mountaineering Equipment. Paths that require the use of via ferrata equipment (ropes, harness, lanyard, helmet, etc.). They can be equipped trails or real via ferratas. It is necessary to know how to use technical equipment safely and to have some familiarity with exposure and mountaineering terrain.

The ones just illustrated are the hiking difficulties, relating to routes that can be covered on foot. Given the lack in Italy of a widespread and shared classification of mountain routes accessible to people with motor impairments, in 2021 the CAI developed a document to classify accessible routes [34].

As explained by Giordana et al. [53] the CAI, which for several years has been promoting projects aimed at PwDs, also by accompanying people with motor impairments in mountain environments, has drawn up this document by setting up a working group extended to experts on the issues of inclusion, integration and sustainability. The following bodies were involved: FISH (Italian Federation for the Overcoming of Handicap), ANTOI (National Association of Italian Technicians and Orthopaedists), SITO (Technical-Scientific Society for Occupational Therapy), SIMFeR (Italian Society of Physical and Rehabilitation Medicine), AIFi (Italian Association of Physiotherapy), FAND (National Federation of Associations of People with Disabilities) and the Piedmont regional directorate of INAIL (National Institute for Insurance Against Accidents at Work).

The CAI “Difficulty Scale”, as presented by Perovani Vicari [54], is a communication tool aimed to accurately and objectively inform those who are preparing to undertake a nature trail or an outdoor activity. It is essential for laying the foundations for a conscious exploration of the places to which it refers. Going into the specifics of the “Difficulty scale for routes with aids”, the parameters were

• Type of route (trail, mule track, etc.). These are standardised, well described and recognisable categories.
• Main features (based on the users): slope, width, difference in altitude, length. Always considered not in general or abstract terms, but specifically observed in relation to the users of the scale.
• Evidence of actual problems: terrain viability, obstacles, problematic points for manoeuvring, and/or exposure. This information is specific for the user/assistant.
• Notes that complete and characterise the whole picture. These are essential to better parametrize the Scale and add information without changing the Scale itself.

The CAI classification of mountain trails accessible with aids (2021) is based on the following three difficulty classes:

• AT = Accessible for Tourists. Routes on dirt tracks or grassy tracks. They are characterised by modest slopes (less than 8%), width greater than 1.5 metres, limited differences in height (less than 150 metres), and length less than 3 km. They generally have a smooth and flowing surface, without artificial or natural steps, without exposed points or tight curves that could make manoeuvring difficult.
  Notes: Although it is possible to overcome small slopes (up to 4 ÷ 5%) independently with a self-propelled wheelchair, it is not advisable to go on mountain routes alone.
• AE = Accessible for Hikers. Routes on clear paths and cobbled mule tracks. They are characterised by moderate slopes (less than 16%), width between one metre and one and a half metres differences in altitude of less than 300 metres, length from 3 to 6 km, uneven surface, few and/or modest artificial or natural steps that can be easily overcome by an off-road auxiliary device, absence of significant obstacles, absence of exposed points and/or tight curves that could make manoeuvring difficult.
  Notes: Regardless of the length of the route, it is necessary to consider the time required to complete the hike in relation to potential issues in the passenger’s permanence on the seat of the aid.
• AEE = Accessible for Experienced Hikers. Routes on mule tracks and paths with traces of passages in varied terrain. They are characterised by some sections with gradients of more than 16%, a width of less than one metre, differences in altitude greater than 300 metres, a length greater than 6 km, a surface that is sometimes uneven and leads to forced passages, natural or artificial steps taller than 10 centimetres, significant obstacles, exposed points and/or tight bends.
  Notes: the presence of at least one of these features makes the route classifiable as AAE, since it requires skills, techniques, experience, and a crew size adequate to overcome the reported difficulties. Regardless of the length of the route, it is necessary to consider the time required to complete the hike in relation to potential issues in the passenger’s permanence on the seat of the aid.

Table 5. “Difficulty scale for routes with aids” by CAI.

		Difficulty Levels
		Accessible to Tourists	Accessible to Hikers	Accessible to Expert Hikers
Characteristics of the trails	Slope	<8%	<16%	>16%
	Width	>1.5 m	1.0–1.5 m	<1 m
	Diff. in altitude	<150 m	150–300 m	>300 m
	Length	<3 km	3–6 km	>6 km
	Surface	Firm and stable	Irregular	Bumpy
	Tread Obstacles	No obstacles	Few natural or artificial steps	Natural or artificial steps > 10 cm; Significant obstacles
Access requirements		Slope < 4 ÷ 5% with a self-propelled wheelchair. Slope > 5% with a single-wheel all-terrain chair, and the help of at least two assistants.	Single-wheel all-terrain chair, with the help of at least two assistants. Evaluation of the hiking time in relation to critical issues	Single-wheel all-terrain chair: requires skills, techniques, experience and an adequately sized crew

summarises the parameters of the “Classification of mountain routes accessible with aids” of the Club Alpino Italiano (CAI).

This difficulty scale focuses mainly on single-wheel wheelchairs (Joëlette) [23], with limited mentions of self-propelled wheelchairs and without considering other types of aids. Furthermore, while it leaves room for evaluation for the classification, it does not specify how many parameters must be satisfied for a given category. A potential improvement would be the inclusion of the average gradient of the route, as it is a useful parameter for a more immediate evaluation of the overall difficulty.

3.3.3. Schweiz Mobil/Svizzera Mobile—Difficulty Levels for “Barrier-Free Routes”

In Switzerland, the principles applicable to networks of pedestrian paths and trails are established by the Confederation. In particular, the planning and quality assurance of trail infrastructures are under the responsibility of the Associazione Sentieri Svizzeri/Schweizer Wanderwege [55] on behalf of the Federal Roads Office (USTRA).

The Schweiz Mobil/Svizzera Mobile Foundation [56] is the official network that, together with the Confederation, the cantons and a number of specialised organisations, manages the site and the app with information on the various routes. Schweiz Mobil in particular has designed a wide range of trails for PwDs [57], thanks to the collaboration with Procap Switzerland [58]. This allows wheelchair users and blind or visually impaired people to discover new hikes and enjoy nature. The routes are also suitable for families with strollers. The route information contains important details about the barrier-free outward and return journey, restrooms, restaurants, parking, overnight accommodation options, as well as information about the place and some tourist attractions.

The “Barrier-free routes” of Schweiz Mobil are classified into three levels of difficulty [39], based on criteria defined in collaboration with various organisations (including Sentieri Svizzeri, Procap Svizzera, Mobility International Switzerland, the Swiss Centre for Disabled-Friendly Construction, Zurich) and by interested parties.

Each level of difficulty considers the length, width, and slope of the route, as well as the characteristics of the road surface and the possible obstacles (

Table 6. Requirements for the difficulty levels of the “Barrier-free routes” adopted in Switzerland.

		Difficulty Levels
		Easy	Medium	Difficult
Characteristics of the trails	Average slope	no significant ascents	<6%	<12%
	Max. slope	8%	12%	20%
	Transverse slope	≤4%	≤6%	≤10%
	Path width	≥1.80 m, narrow spots ≥ 0.80 m	≥1.20 m, narrow spots ≥ 0.80 m	≥1.00 m, narrow spots ≥ 0.80 m
	Nature of the terrain	- Asphalt and concrete surfaces. - Paving slabs and stones with max. 10 mm wide open joints (also applies to planking). - Water-bound natural surfaces (e.g., marl surfaces). Single steps up to 30 mm in height.	- Asphalt and concrete surfaces. - Paving slabs and stones with max. 10 mm wide open joints (also applies to planking). - Water-bound natural surfaces (e.g., marl surfaces). Single steps up to 50 mm in height.	- Asphalt and concrete surfaces. - Paving slabs and stones with max 10 mm wide open joints in the longitudinal direction and max 30 mm wide in a lateral direction. - Water-bound natural surfaces (e.g., marl surfaces). Single steps up to 50 mm in height.
	Conditions	Easy	Medium	Difficult
	Length	up to 4 km	up to 8 km	over 8 km
	Altitude difference	up to 50 metres	up to 100 metres	over 100 metres
	Time required	up to 1.5 h	up to 3.5 h	over 3.5 h
	Nature of the terrain	80% of the route is paved	50% of the route is paved	less than 50% of the route is paved
Access requirements		Suitable for self-propelled wheelchairs	Suitable for self-propelled wheelchairs, for disabled people with a sporting aptitude or accompanied; or for motorised wheelchairs or scooters	Suitable for wheelchair auxiliary drives, such as attachable motors

).

The “easy” level is suitable for anyone who can move around in public spaces without the help of another person. These people also include those who use a wheelchair. The trail has no significant climbs and has a maximum gradient of 8%. On flat sections, isolated steps with a height of up to 30 mm are possible. The “medium” level is suitable for disabled people with a sporting aptitude, disabled people accompanied by an assistant or people with a motorised wheelchair or scooter. For most of the route, the gradient is less than 6% with a maximum gradient of 12%. On flat sections, isolated steps with a height of up to 50 mm are possible. The “difficult” level is suitable for those who use a towing device for wheelchairs. For most of the route the gradient is less than 12% with a maximum gradient of 20%. On flat sections, isolated steps with a height of up to 50 mm are possible.

This difficulty scale considers all types of aids to be used independently but excludes those that require assistance such as single-wheel wheelchairs (Joëlette). A point of strength of this classification is the inclusion of the average gradient of the route, a parameter that provides a more immediate indication of the overall difficulty of the itinerary.

3.4. Synthesis of a Comprehensive Difficulty Levels Classification for Accessible Hiking Trails

The studies analysed in the previous section and sub-sections propose different criteria for evaluating the difficulty of the routes according to objective parameters, such as the maximum slope, the length of the uphill sections between one resting spot and the next one, the type of surface and the general conditions of the path. The difficulty scales developed by Lundell [20], Zeller et al. [21] and Lepoglavec et al. [22] have shown the importance of specific gradient thresholds to determine accessibility levels, distinguishing between routes that can be used independently with a self-propelled wheelchair from those that may require assistance and those that require constant support. The Club Alpino Italiano (CAI) has developed a classification [34] that integrates parameters such as slope, width, difference in altitude, length, type of terrain and presence of obstacles, paying particular attention to feasibility with a single-wheel wheelchair (Joëlette) [23]. A similar classification has been developed by Svizzera Mobile/Schweiz Mobil [39]: in addition to the maximum gradient, it also specifies the average gradient of the route, providing more immediate information on the overall difficulty of the itinerary. The average gradient can also be deduced from the values of the CAI scale, since the latter provides the maximum difference in altitude and the length of the route.

In

Table 7. Comparison table of route classification criteria.

	Characteristics of the Studies
Studies/Criteria	Document Type	Running Tests	Aids	Parameters	Path Category
Lundell, Y. (2005) [20]	Manual	no	- Wheelchair	- Slope - Max. length of segment	- Easy - Moderate - Most difficult
Zeller, J. (2012) [21]	Manual	no	- Wheelchair	- Slope - Max. length of segment	- Easy - Moderate - Difficult - Most difficult
Lepoglavec, K. (2023) [22]	Article	yes	- Wheelchair	- Slope - Macadam surface	- Easy - Moderate - Most difficult
Club Alpino Italiano (2021) [34]	Classification Document	no	- Wheelchair - Joëlette	- Slope - Path width - Difference in altitude - Length - Surface - Tread obstacles	- Accessible to tourists - Accessible to hikers - Accessible to expert hikers
Svizzera Mobile [39]	Manual	no	- Wheelchair - Power Device	- Average slope - Max slope - Transverse slope - Path width - Difference in altitude - Length - Surface	- Easy - Medium - Difficult

, we present a comparison of the various trail difficulty classification systems analysed, highlighting their distinctive characteristics. For each case, the type of document from which the scale is derived is indicated, along with whether field tests were conducted, the mobility aids considered, the parameters used for evaluation, and finally the proposed difficulty categories. This comparison allows for an understanding of the methodological differences between approaches, thus offering a systematic overview of how trail difficulty is defined and represented in relation to accessibility.

The harmonisation of these methodologies stands as a crucial step towards the definition of a shared standard, capable of improving the accessibility of nature trails for all and of promoting the awareness of PwDs in choosing the most feasible path according to their abilities and needs. In

Table 8. Summary of the different classifications of the trails’ difficulty levels with specification of the suitable aids.

		Aids
Difficulty Level	Characteristics of the Trails	Wheelchair	Wheelchair Assistant	Power Device	Joëlette
I	average slope < 5% maximum slope 5% surface: firm and stable	•	•	•	•
II	average slope < 5% maximum slope 9% surface: firm and stable	• *	•	•	•
III	average slope < 6% maximum slope 12% surface: firm and stable		•	•	•
IV	average slope < 10% maximum slope 16% surface: irregular			•	•
V	average slope < 12% maximum slope 20% surface: irregular			•	• **
VI	average slope ≥ 12% maximum slope ≥ 20% surface: bumpy			• ***	• **

* For PwDs with a sporting aptitude. ** With more than two companions. For lower slopes, two companions are sufficient. *** Power Device combined with Rear drive kit.

, we propose a novel scale with six difficulty classes, considering average gradient, maximum slope, and characteristics of the path surface.

For independent use of the self-propelled wheelchair, most studies recommend an average slope lesser than 5% and a maximum slope of 5%, on a stable surface free of protrusions or holes. Above these values, independent use is recommended only for people with a sporting aptitude or accompanied by an assistant, with thresholds between 5% and 10%, according to Zeller et al., and between 5.51% and 9.01%, according to Lepoglavec et al. A maximum slope range between 5% and 9% was considered as a conservative threshold.

The use of the self-propelled wheelchair with assistance is also possible for greater slopes: Zeller et al. suggest values between 10% and 12%, Lepoglavec et al. indicate values above 9.01%, while Svizzera Mobile provides a maximum gradient of 12% and an average gradient of less than 6%. Based on these indications, an average gradient of less than 6% and a maximum slope of 12% were considered in the table.

Concerning the use of the single-wheel wheelchair, according to the CAI scale, it is possible to tackle average slopes of up to 10% and maximum slopes of 16%, even on paths with an uneven surface, with the support of two companions. For slightly higher values, Svizzera Mobile suggests using auxiliary drives for average gradients of less than 12% and maximum gradients of 20%. For values above these limits and on particularly rough terrain, feasibility would require auxiliary drives combined with rear motorization kits, or single-wheel wheelchairs assisted by a team of more than two skilled and experiences assistants.

The experiences of the difficulty scales adopted by the CAI and the one adopted in Switzerland, as well as the values of the slopes for the different difficulty categories proposed in the three studies by Lundell (2005) [20], Zeller et al. (2012) [21] and Lepoglavec et al. (2023) [22], are summarised in Figure 6. As the average gradient and maximum gradient of a trail increase, the range of aids that can be used by people with motor disabilities narrows.

3.5. Guidelines for Accessible Outdoor Services

In the last section, we would like to provide a review of the guidelines for creating accessible and inclusive services related to outdoor activities like hiking, mainly drawn on the principles of Universal Design. These guidelines are intended to help designers and planners to ensure that their projects meet the needs of all users, including those with disabilities, thereby promoting equality and social inclusion.

In 1985 the concept of Universal Design was introduced by the architect Ronald L. Mace of North Carolina State University, who defines it as the design of products and environments that are accessible and usable by all people to the greatest extent possible, without the need for adaptations or specialised aids [59].

Universal Design proposes a new model for designers who must base their work on the needs of the people to whom the project is addressed, including among the recipients also people who live with various disabilities. In the space of twenty years, we have moved from Universal Design to Inclusive Design and Human Centred Design, ultimately reaching the Design for All, i.e., design for human diversity, social inclusion and equality, as stated in the Stockholm Declaration (2004) [60], of the European Institute for Design and Disability:

Design for All aims to enable all people to have equal opportunities to participate in every aspect of society. To achieve this goal, the built environment, everyday objects, services, culture, and information—in short, everything that is designed and made by people to be used by people—must be accessible, convenient for everyone in society to use and responsive to evolving human diversity.

Creating environments free or almost free from barriers, designed to be for all, is the essential premise for ensuring equal rights. The recent EN 17210:2021 standard [61], which is mainly based on ISO 21542:2011 [62], lists the functional requirements of accessibility and usability of the built environment. Moreover, it stands as an important step forward towards the creation of inclusive environments, created with a “Design for all/Universal Design” approach.

This design is identified by compliance with the following requirements:

• Equity, intended as designing for all, regardless of disabling conditions.
• Flexibility, intended as the ability to adapt to different disabling conditions.
• Simplicity and intuitiveness, consisting in the ease of understanding regardless of the user’s experience, knowledge, linguistic skills or level of concentration.
• Information perceptibility, consisting in the effective communication of necessary information to the user, regardless of environmental conditions or sensory capabilities.
• Tolerance for error, consisting in the minimization of dangers and adverse consequences of accidental or unintended actions.
• Reduction in physical effort, consisting in using the design efficiently, comfortably and with a minimum of fatigue.
• Size and space for approach and use, consisting in making the space easily usable regardless of the user’s body size, posture, and abilities.

The document does not prescribe or describe how these functional requirements should be met and is therefore not intended to conflict with national accessibility standards.

However, apart from interventions in urban areas (where accessibility is well codified for buildings and public roads), national and international technical standards and regulations for the accessibility of hiking trails, active tourism and nature-based tourism appear to be fragmented and incomplete, almost totally lacking complete references.

That is why some national or supranational agencies and organisations have published documents with Guidelines for accessibility to trails and outdoor recreational activities under their jurisdiction.

In the UK, one of the most significant efforts to create a national set of standards for physical access in the countryside has been the BT Countryside for All Accessibility Standards, Fieldfare Trust (1997 and 2005) [26]. These guidelines are intended to assist natural area managers in making informed decisions about accessibility on country trails.

Part of the research was developed with the aim of identifying accessibility standards for trails depending on the different natural contexts in which they are located. In particular, four different rural environments have been defined:

• “Urban and formal landscapes”, e.g., countryside areas with many man-made features;
• “Urban fringe and managed landscapes”, e.g., countryside areas near towns or outdoor recreation areas;
• “Rural and working landscapes”, e.g., farmland and woodland;
• “Open Country, semi-wild and wild”, e.g., mountains, moorlands, and remote countryside.

The BT Countryside for All accessibility standards are defined primarily in terms of physical access and predominantly in relation to people with motor impairments who use aids such as wheelchairs, walking frames or crutches. The standards cover path surfaces, widths, barriers, double wheelchair treads, resting spots, slopes, tread obstacles, and tread surface openings, and vary across different environments. Regulations are more restrictive in urban landscapes and less stringent in remote countryside, as people accept that the countryside is less accessible than the city. In fact, a walk in the open air offers a very different experience, e.g., among a walk in the park, a countryside hike, or a trek in the mountains. Precisely for this reason, the only rural environment not subject to defined technical specification is the “open country, semi-wild and wild”, a place with objective morphological difficulties that people do not expect to be modified to allow accessibility. In any case, if works were to be conducted in this context to enable accessibility, the least restrictive standards, i.e., those for “rural and working landscapes”, must be met.

In Sweden, on behalf of the National Board of Forestry in Sweden, Lundell (2005) has published the manual “Access to the forests for disabled people” [20]. The manual focuses primarily on the needs of people with motor disabilities, especially those who use wheelchairs (self-propelled or electric), but also those with motor impairments, short people and people with limited arm and leg functions. The document provides general information on parking areas near outdoor recreational areas (with spaces reserved for PwDs), gates and barriers to control access to trails, and the characteristics of information panels and signage. Specific technical requirements for the trail are also provided, such as the type of surface, minimum width, width for two wheelchairs to meet, slopes, resting intervals, dimensions of bridges for crossing watercourses and walkways for unstable terrain. A section of the document is then dedicated to some recommendations for other activities in nature, such as water sports and winter sports, which go beyond the topic covered in our study. This manual also emphasises the importance of preserving the original environment along the trail as much as possible, so as not to lose the experience of nature and therefore the entire scope of the project.

In the United States, Zeller et al. (2012) developed for the United States Department of Agriculture (USDA) Forest Service an “Accessibility Guidebook for Outdoor Recreation and Trails” [21]. These guidelines are legally enforceable on National Forest System lands: those working with or for the Forest Service on National Forest System lands must comply with the applicable guidelines and standards when designing, constructing, or modifying any structure or component covered by these standards on National Forest System lands. While the guidelines are in place for the Forest Service only, they contain useful concepts that may help other agencies and organisations to maximise the accessibility of outdoor recreation areas and trails while protecting the natural features of the places. In relation to designing routes for use by hikers, including those with reduced mobility, who use wheelchairs or other aids, the document defines the various technical accessibility requirements to be compliant with. Specifically, these are characteristics and measurements regarding the surface or pavement of the trail, the clear width of the tread, the longitudinal and transverse slope, rest intervals, passage spaces, obstacles in the tread, openings in the tread surfaces, objects protruding onto the trail, trail start signs, gates, and barriers for controlling access to the trails. To ensure that the unique features of the natural environment and recreational opportunities on the trails are not compromised or substantially altered, exceptions and deviations from some technical requirements are permitted when exceptional circumstances and conditions apply. The first of these conditions applies in the case of actually inaccessible terrain and excessive slopes. The second—when compliance with the technical requirements would unacceptably modify the place. The third—when compliance with the technical requirements cannot be achieved with prevailing construction practices, whilst the fourth when significant cultural, historical, or natural features shall be protected.

In Ireland, the “Great Outdoors—A guide to accessibility” (2018), produced by the Irish Wheelchair Association in collaboration with Sport Ireland [28], builds on the concepts of BT Countryside for All [26] and the work of Lundell in Sweden [20], with the aim of providing organisations and land managers with guidance and information to make their specific environments more accessible for PwDs. The guidelines set out in this document apply to public trails/greenways/parks, beaches, and waterways. The document proposes specific and practical solutions that need to be provided to improve the accessibility of these three different outdoor environments. In particular, the first section considers how accessibility can be integrated into the design and management of trails, greenways, and public parks, including any facilities such as picnic areas and playgrounds on site. Since greenways are very important attractions in public parks, trails are a major focus of this section which provides design criteria for making them accessible. The document provides information on the type of surface, the minimum width, the width for two wheelchairs to meet, the slopes and the resting intervals. In particular, two different levels of accessibility are defined. Firstly, the “Multi-Access path” which is free of obstacles along its entire length and has a solid, flat, and wide surface. Secondly, the “Challenging Access path”, which instead has more significant gradients, with a surface that is not always solid and has reduced widths in some points according to defined standards. In addition, these guidelines propose the adoption of the international wheelchair symbol to identify the two levels of accessibility on trails and paths according to their different standards. These signs should be placed at the beginning of the trail and at all access points, accompanied with directional arrows to indicate the trail.

In Greece, the National Confederation of Disabled Persons (2019) has produced a “Guidebook for Accessible Nature Trails—Design Guidelines and Evaluation System” [27]. This work is the result of an Interreg project in Greece and Bulgaria aimed at the improvement and promotion of nature trails in the two countries, with the main goal of making such trails accessible to “the greatest possible number of visitors, including people with reduced mobility”. The text is divided into two sections: the first provides guidelines for making these trails accessible, while the second one presents a system for evaluating accessibility after the implementations recommended by the project have been made. After an introductory section containing a glossary of several key terms and the definition of the characteristics and needs of PwDs (including people with various forms of intellectual disability), the document provides the guidelines for designing accessible nature trails. These guidelines are recommendations compliant with the legal obligations arising from the technical regulations of both countries on the accessibility of buildings and public roads. Moreover, specific standards for the use of nature trails by people with reduced mobility who use wheelchairs or other auxiliary devices are also included. In particular, these technical features build on the work of Zeller et al. [21], developed for the U.S. Department of Agriculture’s Forest Service (Accessibility Guidebook for Outdoor Recreation and Trails), covering trail surface or pavement, clear tread width, longitudinal and transverse slope, resting intervals, clearances, tread obstacles, openings in tread surfaces, and protruding objects on the trail. Details are also provided on how to improve the effectiveness of signage for a variety of users.

From this overview on guidelines, we shall conclude that some studies also underline the importance of sustainability in interventions for accessibility. The research by Darcy et al. [35] highlights that accessibility should be developed in synergy with sustainability, aiming at a tourism that not only breaks down architectural barriers, but also adopts ecological practices that reduce environmental impact and promote a responsible development of natural areas. The study by Garrod et al. [36] adds further value to the debate, suggesting a gradual and progressive approach based on the implementation of small targeted interventions capable of triggering a positive domino effect on overall accessibility. This strategy also focuses on safeguarding the integrity of natural areas, avoiding invasive interventions in accordance with the “not paving paradise” principle, and aiming to offer PwDs not only a physical access, but an authentic way to enjoy nature.

3.6. Inclusive Planning and Local Services

The development of accessible tourism in nature stands as a significant opportunity, not only from an economic point of view, but above all to promote social inclusion and break down physical and cultural barriers. However, accessibility remains a complex challenge that requires a holistic approach based on the principles of universal design. As reported in the literature, including the article by Wall-Reinius et al. [24], accessibility cannot be conceived as a series of isolated interventions, but as a chain in which every element of the tourist experience must be accessible. Efforts are concentrated on single activities or infrastructures; therefore, there is the risk of nullifying the progress made so far.

An accessible nature trail loses value if it lacks adequate means of transport, accommodation facilities and services. Godtman Kling et al. [16] highlight how even sought-after destinations such as natural parks are often plagued by disconnections among the various aspects of accessibility. Without a consistent integration, the tourist experience of PwDs may be compromised.

A key element to ensure inclusive access to natural parks concerns public transport and dedicated parking infrastructure. As highlighted in the study by Shen et al. [7], the presence of accessible transport and reserved parking is crucial to encourage the participation of PwDs in outdoor activities. The lack of accessible public transportation, or the lack of parking near entrances and trails, can be insurmountable barriers for many visitors. Another element of great importance is the availability of accessible toilets along the routes and in natural parks. According to the study by Błaszczyk et al. [5], the lack of adequate toilet facilities is perceived as one of the main barriers for PwDs in nature. The provision of accessible, well-placed restrooms at strategic points throughout parks and trails not only improves accessibility, but also makes the experience more comfortable and decent for all visitors.

In addition to these infrastructural elements, it is important to provide clear and transparent information: as reported in the article by Corazon et al. [15], the lack of accurate information on tourism-centred websites and information systems is often as much of a barrier as physical infrastructure. Visitors with disabilities need an easy access to detailed information to plan their experience in an informed and autonomous way. In addition, the promotion of tourist attractions must emphasise the aspects related to accessibility. As highlighted in the article by Cloquet et al. [33], many promotional campaigns fail to consider the disabled public, relegating accessibility information to a marginal role or completely ignoring it in both texts and images of brochures and websites. Benjamin et al. [31] report how images and texts referring to PwDs rarely appear in the promotional materials of many destinations, thus discouraging potential visitors with disabilities who may perceive the destinations as unwelcoming or unprepared to meet their needs. Including this type of content in tourism marketing materials not only reinforces the image of inclusive tourism, but also conveys a sense of welcome and belonging, contributing to a greater social awareness towards disability.

In the design stage of infrastructures, the direct involvement of PwDs is very important, as reported in the article by Groulx et al. [25]. A participatory approach from the early design stages ensures that trails, facilities, and services are truly inclusive. Including people with different types of disabilities allows for identifying and overcoming barriers that are invisible to designers without disabilities, ensuring functional and effective solutions.

Faced with these needs, public bodies have a duty to adopt collaborative policies, since many small nature-based tourism companies do not have the resources needed to implement large-scale solutions. Chikuta et al. [32] highlight the importance of public support to facilitate cooperation between different actors in the industry and ensure an accessible tourism ecosystem.

Another essential issue is the training of tourist staff and facility managers. Many service providers are not prepared enough to understand and respond to the specific needs of PwDs. As pointed out by Wall-Reinius et al. [24], lack of awareness and specific skills can represent as much of a barrier as physical infrastructure. Training staff to recognise the needs of visitors with disabilities, how to accommodate them, and create an inclusive environment is essential for improving the overall experience.

Shen et al. [7] and Godtman Kling et al. [16] highlight how technology plays a key role in increasing accessibility for visitors with disabilities, improving both the overall experience in parks and the information available before the visit. Mobile apps and interactive maps provide up-to-date information on accessible routes and specific services, such as parking and barrier-free restrooms. Assisted navigation systems, using GPS and proximity sensors, which support visitors with visual or motor impairments during their visit. The article also mentions the adoption of virtual reality, which allows persons with physical limitations to explore otherwise inaccessible areas. Finally, advanced mobility devices, such as all-terrain wheelchairs, that allow for accessing more challenging routes, are becoming more popular.

In short, a paradigm shift is needed to ensure the success of accessible nature tourism. Agovino et al. [18], accessibility should not be seen as a concession, but as a fundamental right. A tourism ecosystem in which every part of the experience is accessible to all visitors, regardless of their abilities, requires an integrated approach that involves PwDs, service providers and public bodies. Only in this way nature-based tourism can become a fully inclusive experience.

4. Conclusions

In the present study, our goal has been to review the state of the art about scientific research, guidelines, design approaches and tools on which public bodies can rely to improve accessible nature-based tourism. Among the key actions to achieve this objective, it is essential to reduce accessibility barriers for people with disabilities (PwDs), both through the adaptation and improvement of trail conditions and by ensuring clear information on the difficulties that hikers may encounter in relation to the use of specific aids. In this perspective, our contribution focused on the harmonisation and synthesis of the different difficulty scales identified in the literature. We have presented them in a single comparative table that defines a novel scale to classify difficulty levels of hiking trails according to the specific mobility aids that can be used for safely access them.

The accessibility of trails and natural areas for people with motor disabilities stands as a crucial challenge, not yet fully resolved. From the literature review and document analysis discussed in the present study, it is clear that, despite technological advances in mobility aids and public initiatives, there are still numerous obstacles that limit the autonomy and inclusion of these people in hiking routes.

The survey allowed us to identify four main areas of intervention: aids for accessing the routes, classifications of the routes for PwDs, guidelines for the accessibility of the paths, complementary local services.

Major support devices, i.e., auxiliary drives and single-wheel wheelchairs such as the Joëlette, are effective solutions for improving accessibility. However, these solutions are not enough. These technologies must be combined with an inclusive planning of routes, as well as the usability of all elements of the “tourist service chain”: accessible transportation, suitable accommodation facilities, reserved parking, and suitable toilets.

Another essential element is a clear classification of the difficulty of the paths, to allow people with motor disabilities to plan their hikes safely and with greater peace of mind. The examined literature proposes different criteria for evaluating the difficulty of the routes, based on objective parameters. The difficulty scales developed by Lundell [20], Zeller et al. [21], Lepoglavec et al. [22], Club Alpino Italiano [34] and Svizzera Mobile [39] provide significant contributions, however each study is limited to a specific mobility aid or in few cases two of them. In this context, our contribution has focused on providing a synthesis of the previously mentioned studies by defining a harmonisation of the scales in question. We have been aiming to offer a comprehensive overview that could help with the definition of a shared standard. An objective and easy-to-understand difficulty levels scale would promote a greater awareness for PwDs in choosing the paths that they can visit according to their abilities, aids, and needs.

Future research in this field should systematically address the challenge of classifying the difficulty levels of hiking trails accessible to PwDs. Although some studies have begun to define objective parameters through empirical testing, the literature still lacks a sufficient number of rigorous investigations to establish scientifically validated criteria. This gap is particularly significant given the wide variability of influencing factors, including the type of mobility aid used, the weight of the user, the slope of the trail, and the roughness of the terrain. To develop reliable and standardised classification systems, a series of empirical studies is needed to collect robust data across diverse conditions. Such efforts would support trail designers in adapting routes more effectively and in providing clear, comprehensible information that empowers users to plan and undertake their hikes with confidence and peace of mind. These kinds of studies are also required for the development of useful guidelines to improve the management of parks and green areas, making them safer and more sustainable, and helping policy makers and designers to create more accessible and inclusive nature trails for PwDs.

Starting from these considerations, we have planned to conduct a systematic experimental campaign focused on the use of single-wheeled wheelchairs, and particularly the Joëlette, a widely used device that allows users to tackle significant slopes. Currently, the data on its operability provided by the Italian Alpine Club are based mainly on practical experience, without the support of rigorous experimental analysis.

Another important issue is the involvement of PwDs in the design of the “tourist service chain”. The needs of PwDs are often very specific, and only through their active participation in the design process is it possible to create routes and infrastructures that truly respond to their needs. The same applies to the training of tourism operators: awareness and the ability to respond to the needs of each visitor are key elements to ensure a truly inclusive experience.

In short, accessibility in nature is not just about eliminating physical barriers, but also involves a cultural shift. Making nature accessible to all is a goal that requires collaboration between institutions, organisations, and private actors. It is the only way to build a more inclusive tourism, where people with motor disabilities can experience nature with the same freedom and autonomy as everyone else.