Sustainability Assessment Indicators in Land Transportation

Abstract

Transportation is vital to life in society; it enables economic, social, and environmental development through connections between areas, cities, and countries, facilitating interactions and integrations. However, transportation is one of the sectors that most impacts sustainability, causing, among other things, emissions of gases, noise, and accidents. Through an integrative bibliographic framework, this study aims to assess the indicators used to evaluate the sustainability of land transportation in various contexts. To this end, relevant papers were selected with intuition to present their main characteristics, and through correlations between the variables analyzed, a framework was built indicating the current situation and future perspectives of the study. In terms of results, some common points were identified among papers, and some categories were pointed out as priorities for a future research agenda, such as the lack of standardization of indicators regarding metrics and nomenclature to emphasize sustainability. A lack of studies covering sustainability as a whole was found, which limits the results of sustainability assessments by only focusing on classic indicators and their deficiencies in relation to social inclusion, political–legal issues, and civil and human rights, as well as the standardization of indicators in other specific sectors.

1. Introduction

Today, transportation is vital to life in society [1]. It is through transportation that economic, social, and environmental development is allowed [2], through connections between areas, cities, and countries, facilitating interactions and integrations through mobility [3]. Because it is so important to life in modern society, it becomes essential. However, transportation has impacts on sustainability, both in the economic and social as well as in the environmental spheres [4,5].

Transportation is one of the most impactful sectors regarding sustainability [6], being one of the main sectors that generate greenhouse gas emissions [7] and therefore responsible for climate changes [8]. In addition, there is a deficit in the socialization of transportation that generates inaccessibility, accidents, noise, and social inequalities [9], which are unsustainable for society. The sustainability of transportation should be a topic of great importance for the main government managers and the whole of society [10].

Sustainable transportation can be defined as the possibility of meeting the current needs of locomotion and mobility without interfering with future needs [11], while maintaining a balance among the economic, social, and environmental dimensions [12]. This would be in line with the main definition of sustainability stated in the Brundtland report [13]. However, the limited use of these three dimensions has generated divergence among researchers; some point out that sustainability goes beyond these three dimensions, as mentioned by Macedo et al. [14], warning of the existence of another dimension: the cultural.

On the one hand there is great concern for sustainable transportation development. Medlol and Alwash [15] point out that an efficient transportation system is a major part of sustainable development. On the other hand, sustainability in transportation has not advanced enough to enable sustainable development [16].

For monitoring the level of transportation sustainability, there must be evaluations. Transportation sustainability assessments should use scientific methods that would enable the analysis and measurement of the sustainability level of this sector [17]. To this end, it is important to identify the current propositions of sustainability assessment for land transportation.

The challenge that arises with sustainable transportation is how to evaluate the level of sustainability of this sector [18,19], due to the complexity that connects other sectors and the fact that sustainability encompasses several dimensions [20]. The evaluation of transportation sustainability may be useful for society representatives, as they assist with information on decision-making and planning regarding sustainable development [21].

Two of the most used methods for the evaluation of sustainability are indicators and indexes, considered accepted as effective methods for measuring a phenomenon [22,23]. These enable statistical monitoring towards the desired outcome [24,25].

The major obstacle has been developing indicators that can measure the level of transportation sustainability [26]. This is because there has been no consensus among the parameters used to evaluate the sustainability of transportation with indicators that are scientifically accepted [27,28].

Thus, in view of the complexity and relevance of this theme, this study aims to analyze, through an integrative bibliographic framework, the propositions of the evaluation of terrestrial transportation sustainability and, through correlations between the variables analyzed, to present the indicators used to evaluate the sustainability of land transportation in various contexts. To this end, relevant papers were selected with intuition to present their main characteristics, and through correlations made between the variables analyzed, a framework indicating the current situation and future perspectives of the study is presented.

To achieve the proposed objective, the methodological procedures, including the research steps and the coding and classification of the data, are presented in Section 2. Section 3 shows the results of the integrative literature review. A framework presenting a synthesis of the main results obtained in the literature systematization on the assessment of sustainability is presented in Section 4, and the main conclusions are presented in Section 5.

2. Methodological Procedures

The purpose of this integrative literature review is to synthesize, evaluate, and integrate previous research on the specific topic, in order to provide an overview of the current state of knowledge. This integrative review seeks to include relevant empirical, theoretical, and conceptual studies, not just those with a particular method or approach, and seeks to identify gaps in knowledge, highlight standards and inconsistencies in existing research, and identify questions for future research [29,30,31,32,33,34].

This integrative review presents an in-depth analysis of the main studies that deal with the current state of sustainability in transportation. In this research, the methodological procedures proposed by Lage Junior and Godinho Filho [35] were adapted to the specific demands of this study, which are divided into six systematic work steps.

The first step was to conduct a bibliographic survey on articles with the theme “practices, indicators, and sustainability rates in transport”; these keywords are the consensus when used as a method of evaluation [36].

The Scopus and ScienceDirect database consultation was held from April to June 2022. The keywords researched were the following: “Transport and Sustainability Practices”, “Transport and Sustainability Indexes”, “Transport and Sustainability Indicators “and” Transport and Sustainability Index”.

Only the articles relevant to this study proposal that were available for download were considered. Due to the large number of results, 300 articles classified by relevance from each database and keyword search were analyzed. Through this selection based on keywords, we found 285 articles.

The second step was to analyze the summary and select only the studies on the evaluation of land transportation sustainability through indicators, indexes, and practices. Studies deemed not relevant were excluded, leaving 100 articles that were fully analyzed. In this study, we used “Sustainability Indicators” to represent “Sustainability Indicators, Indexes, and Practices”.

The third step consisted of mapping each paper onto the indicators, indexes, and practices used to evaluate the sustainability of transportation: the analysis tools, the country focus, the mode of transportation, the keywords, the authors, the year of publication, the category of the sustainability dimension analyzed, and the publication journals.

In the fourth step, a classification system was developed with logically structured coding for the categorization of the analyzed variables.

The coding of the indicators was elaborated from groups and subgroups due to the extensive list of identified indicators: 1202 (Appendix E) groups were categorized in alphabetical order (groups from A to AY) and subgroups were categorized in numerical order (e.g., group A, subgroups A1, A2, and A3), as shown in

Table 1. Classification and coding of indicators.

Group	Cod.	Subgroup	Cod.	Description
Accessibility	A	Physical accessibility	A1	Includes indicators that evaluate the accessibility related to the conditions of the structure and the modes of transportation in adaptability to meet the various conditions of the passengers.
		Accessibility of range	A2	Includes indicators that evaluate the accessibility related to the proximity of transportation to serve passengers to their destinations.
		Tariff accessibility	A3	Includes indicators that evaluate the conditions of passengers to pay for the ticket or have free access to modes of transportation.
Traffic accidents			B	Includes indicators that evaluate and measure accidents and fatalities caused by traffic.
Transportation worker social benefit			C	Includes indicators that evaluate the benefits received as transportation workers.
Transportation companies and subsidies	D	Benefits	D1	Includes indicators that evaluate and measure the type and number of investments and resources received (direct and indirect) by companies that perform transportation.
		Subsidies	D2	Includes indicators that evaluate and measure the subsidies received for transportation.
Technical characteristics of transportation modes			E	Includes indicators that evaluate and measure the characteristics of vehicles that perform transportation.
Environmental certification			F	Includes indicators that evaluate and measure the types of environmental certification given to companies that perform transportation.
User awareness			G	Includes indicators that evaluate user awareness of the content of economic, environmental, and social sustainability.
Energy consumption, fuel, and natural resources	H	Energy consumption	H1	Includes broad indicators that evaluate and measure the general amount of energy consumed in transportation and transportation infrastructure.
		Renewable energy consumption	H2	Includes indicators that evaluate and measure the amount of renewable energy consumed in transportation and transportation infrastructure.
		Non-renewable energy consumption	H3	Includes indicators that evaluate and measure the amount of non -renewable energy consumed in transportation and transportation infrastructure.
		Fuel consumption	H4	Includes indicators that evaluate and measure the fuel quantity consumed in transportation.
		Natural resource consumption	H5	Includes indicators that evaluate and measure the amount of natural resources consumed in transportation and transportation infrastructure.
Costs	I	Costs	I1	Includes broad indicators that evaluate and measure the costs of general spending for transportation.
		Fixed cost	I2	Includes indicators that evaluate and measure the costs that are constant regardless of the amount of transportation performed.
		Variable cost	I3	Includes indicators that evaluate and measure the costs that change due to transportation execution.
Demand			J	Includes indicators that evaluate and measure the demand for transportation of companies that perform this activity.
Expenses			L	Contemplates the indicators that evaluate and measure spending on the management and maintenance of companies that perform transportation.
Availability and diversity of mode	M	Transportation availability	M1	Includes indicators that evaluate and measure the availability of transportation for users/customers.
		Modal diversity	M2	Includes indicators that measure and evaluate the types of modes that include the needs of users/customers.
Civil and human rights			N	Contemplates the indicators that evaluate the transportation practices of transportation companies regarding the treatment of the civil and human rights of users, customers, and workers.
Efficacy and efficiency of the system	O	Effectiveness of the system	O1	Includes indicators that evaluate and measure whether the transportation system has fulfilled the proposed objective or has reached its desired result.
		System efficiency	O2	Includes indicators that evaluate and measure whether the transportation system has fulfilled its activity in the best way, with quality, competence, and excellence.
Geographic space			P	Includes indicators that evaluate and measure the coverage of the transportation system in relation to geographical demarcations.
Minimum transportation mode specifications			Q	Contemplates the indicators that evaluate and measure the minimum specifications of the modes of transportation for users and their needs.
Management	R	Environmental management	R1	Includes indicators that evaluate the good environmental practices of companies that perform transportation.
		Economic management	R2	Includes indicators that evaluate the good economic management practices of companies that perform transportation.
		Social management	R3
Equality and equity	S	Equality	S1	Includes indicators that evaluate the good social management practices of companies that perform transportation.
		Equity	S2
Environmental impact	T	Environmental impact	T1	Includes indicators that evaluate equality in relation to the practices of the transportation company acts before its employees and users.
		Climate changes	T2	Includes indicators that evaluate equity in practical relations of the transportation company acts before its employees and users.
		Mode efficiency	T3	Includes indicators that evaluate the environmental impacts generated due to transportation.
		Energy efficiency	T4	Includes indicators that evaluate the impacts resulting from transportation that alter the environment.
Economic impact	U	Economic development	U1	Includes indicators that evaluate the resulting impact of the types of modes used for transportation that impact the environment.
		GDP	U2	Includes indicators that evaluate the resulting impact of the energy types used for transportation that impact the environment.
Social impact	V	Social effect	V1	Includes indicators that evaluate and measure the impact of transportation in relation to local economic development.
		Job	V2	Includes indicators that evaluate and measure the economic impact of transportation in relation to GDP.
Taxes			W	Includes indicators that evaluate the social impact caused by transportation.
Information and signaling	X	Information	X1	Includes indicators that evaluate and measure generation and maintenance jobs in the transportation sector.
		Signs	X2	Contemplates the indicators that evaluate and measure the collection from the transportation sector to the public coffers.
Infrastructure	Y	Bike lanes	Y1
		Network density	Y2	Includes indicators that evaluate the level of information to users relating to the transportation mode, frequency, times, and transportation stops.
		Parking	Y3	Includes indicators that evaluate and measure the quantity and proportion of parking in the transportation network.
		Road	Y4	Includes indicators that evaluate and measure the extent and quality of the roads in the transportation network.
		Exclusive bands	Y5	Includes indicators that evaluate the level, proportion, and quantification of exclusive lanes by transportation mode in the transportation network.
		Installations	Y6	Includes indicators that evaluate the level, quality, and proportionality of the transportation network facilities.
		Transportation network	Y7	Includes indicators that evaluate the components that make up the transportation network.
Innovation and technology			Z	Includes indicators that evaluate the innovations and technologies used that facilitate use of users, improves the management of transportation companies, and optimizes the transportation network.
Interconnectivity and intermodality			AA	Contemplates the indicators that evaluate the interconnectivity and intermodality of transportation.
Mobility			AB	Contemplates the indicators that evaluate the displacement between one point to another (urban mobility) in relation to transportation.
Motorized modes			AC	Contemplates indicators that evaluate and measure the proportion of non-motorized modes in cities.
Occupation and capacity of transportation mode	AD	Mode occupation	AD1	Includes indicators that evaluate and measure the proportion between the capacity that each mode of transportation has with effective transport.
		Mode capacity	AD2	Includes indicators that evaluate and measure the capacity that each transportation mode has in execution.
Civil community participation in management			AE	Contemplates the indicators that evaluate the community’s level of participation in transportation decisions in the city.
Public policy	AF	Environmental policy	AF1	Includes indicators that evaluate the level and effectiveness of the policies implemented in the environmental area.
		Price policy	AF2	Includes indicators that evaluate the level and effectiveness of price policies in the economic area.
		Monetary policy	AF3	Includes indicators that evaluate the level and effectiveness of monetary policies implemented in the economic area.
		Budget policy	AF4	Includes indicators that evaluate the level and effectiveness of budget policies implemented in the economic area.
		Planning policy	AF5	Includes indicators that evaluate the level and effectiveness of public policies implemented for planning.
		Social policy	AF6	Includes indicators that evaluate the level and effectiveness of policies implemented in the social area.
Pollution	AG	Air pollution	AG1	Includes indicators that evaluate and measure gas emissions that affect air quality.
		Water pollution	AG2	Includes indicators that evaluate and measure waste emissions that affect water quality.
		Ground pollution	AG3	Includes indicators that evaluate and measure waste emissions that affect soil quality.
		Noise pollution	AG4	Includes indicators that evaluate and measure noise emissions that affect the environment and living beings.
Punctuality			AH	Contemplates the indicators that evaluate and measure the punctuality of transportation.
Cultural preservation			AI	Includes indicators that evaluate the impact of transportation on cultural preservation.
Social projects			AJ	Includes the indicators that evaluate the level of companies that perform transportation in the implementation of social projects in communities.
Environmental protection			AL	Contemplates the indicators that evaluate the practices of companies that perform transportation in environmental protection.
Quality of life			AM	Contemplates the indicators that evaluate the quality of life of the community and transportation users.
Qualification of workers			AN	Includes the indicators that evaluate the qualification given by the companies that operate transportation to their employees.
Recycling			AO	Contemplates the indicators that evaluate and measure the recycling carried out by the transportation companies.
Regulation of standards and laws			AP	Contemplates the indicators that evaluate the companies that operate in transportation on compliance with the rules and laws.
Satisfaction and quality	AQ	Transportation and infrastructure	AQ1	Includes indicators that evaluate the conditions of transportation and infrastructure services.
		Transportation reliability	AQ2	Includes indicators that evaluate users’ confidence in transportation.
		User/customer Satisfaction	AQ3	Includes indicators that evaluate the satisfaction of users and customers about transportation.
Health			AR	Contemplates the indicators that evaluate the health conditions of employees, users, and customers due to transportation execution.
Security			AS	Includes the indicators that evaluate the safety conditions of employees, users, and customers due to transportation execution.
Duration and distance from travel	AT	Travel duration	AT1	Includes indicators that evaluate and measure the duration of travel or transportation.
		Trip distance	AT2	Contemplates indicators that evaluate and measure the distance traveled from transportation or travel.
Traffic			AU	Contemplates the indicators that evaluate and measure traffic conditions in cities and on roads.
Soil use			AV	Contemplates the indicators that evaluate and measure the use of soil for transportation and its infrastructure.
Added value			AW	Contemplates the indicators that evaluate and measure the added value of transportation.
Private vehicles			AX	Contemplates the indicators that evaluate and measure the proportion of private vehicles in transportation.
Financial evaluation	AY	Viability	AY1	Includes indicators that evaluate and measure the financial/economic condition of the transportation service.
		Revenues	AY2	Includes indicators that evaluate and measure the revenues collected from the transportation service.
		Productivity	AY3	Contemplates indicators that evaluate the measure of the production of the transportation service.

.

The coding of study focuses was organized with the code “FC” varying in numerical order (FC1 to FC19), according to Appendix A. Each study can have more than one objective focus.

The codification of the analysis tools was performed using alphabetical order, with the “Ant_” code and the letter indicating the alphabetical order, according to Appendix B.

The coding of the types of transportation was performed through the identification and classification of groups. The groups were codified by unit (Un), type (Ty), modality (Mo), transported category (Ca), sector (Se), transportation mode (Mt), and transportation locality (Lo). The subgroups were classified by numerical order, as shown in Appendix C. It is noteworthy that each study can include more than one group, of which the total will indicate the specificity of transportation.

The fifth step consisted of applying the classification system to selected articles in order to structure the existing knowledge on the studied theme and present the relevant profile through its main results.

The sixth step comprises the analysis of results and the presentation of gaps, opportunities, and challenges for future studies.

3. Results of the Integrative Literature Review

Through an integrative review of the literature, we analyzed the articles relevant to our purpose regarding practices, indicators, and indexes of sustainability in land transportation. Appendix D presents the classification and coding applied to the selected studies, and the Figure 1, Figure 2, Figure 3 and Figure 4 were built from the analysis and correlations of the information.

From the results, it was found that most of the analyzed articles (78%) were published in journals with index Q1, which states the quality of the articles under study. Of the total, 45% of the articles are in journals with an SJR indicator greater than 1. The journals that published the most articles on this study theme were Sustainability (15%), Ecological Indicators (9%), Case Studies on Transportation Policy (7%), Journal of Cleaner Production (7%), and Transportation Research Procedures (7%).

The most frequently used keywords in studies are “Sustainability”, “Sustainable Transportation”, and “Public transportation”.

There has been exponential growth in the theme of sustainability indicators in land transportation in recent years, where 53% of the articles published over the last 3 years (from 2020 to 2022) were in this theme.

India (10%) and Brazil (8%) showed the highest concentrations of studies on the theme of sustainability indicators in land transportation, followed by the United Kingdom (5%), Taiwan (5%), China (4%), Australia (3%), Canada (3%), and Sweden (3%), and 14% of studies were conducted in more than one country, mostly in Europe (25%).

The dimensions of sustainability (Figure 1) identified in this survey are as follows: environmental (31.70%), social (30.75%), and economic (26.23%), totaling the Triple Bottom Line with 87.4%. In addition to these, other dimensions were identified to compose the sustainability of transportation: accessibility (2.83%), policy (0.57%), technological (0.57%), legal (0.57%), the technician (1.13%), energy (0.94%), financial (0.38%), system effectiveness (0.57%), innovation (0.38%), activity (0.19%), system efficiency (0.75%), performance (0.75%), resource (0.57%), climate (0.57%), and quality (0.57%).

A total of 19 categories of study focus (Appendix A and Figure 2) were identified, of which 3 groups concentrate most publications (65.34%): FC6 (33.19%), which analyzes an urban region, FC4 (18.10%), which presents the sustainability indicators, and FC7 (14.05%), which presents the consideration of the indicators through experts. The less studied study focuses were FC12 (0.48%), which analyzes the coverage of the transportation network, FC9 (0.97%), which classifies transportation by type in relation to sustainability, FC13 (0.97%), which presents more sustainable modes of transportation, and FC15 (0.97%), which reviews the definitions of sustainability.

This integrative review of the literature cataloged 1202 (Appendix E) different indicators, which differ in the metric or nomenclature, but most resemble each other in essence. Thus, there was a need to create groups and subgroups for the framing of these indicators (Table 1 and Figure 3).

The groups of indicators (Table 1 and Figure 3) with higher frequencies (58.13%) among the articles are as follows: AG (pollution; 10.81%), A (accessibility; 9.3%), H (energy consumption, fuel, and natural resources; 5.95%), Y (infrastructure; 5.36%), I (costs; 4.86%), AQ (satisfaction and quality; 4.37%); M (availability and diversity of modes; 3.87%); AS (security; 3.57%); T (environmental impact; 3.47%); AD (occupation and capacity of transportation modes; 3.37%), and B (traffic accidents; 3.37%). It is worth mentioning the subgroup AG1 (air pollution), with 66.99% from the AG group and 7.24% of the overall from groups and subgroups.

The groups of indicators with lower frequencies (3.08%) are as follows: AJ (social projects; 0.20%); AW (value added; 0.30%); F (environmental certification; 0.30%); Q (minimum specifications of transportation mode; 0.30%); AI (cultural preservation; 0.40%); AL (environmental protection; 0.40%); C (social benefit of transportation worker; 0.40%); N (civil and human law; 0.40%); and P (geographical space; 0.40%). The subgroups that have lower frequencies in relation to the total (groups and subgroups) are as follows: AF3 (monetary policy) with 0.10%, which comprises group AF (public policy) with only 4.35% in appearances in this group.

From the 49 groups of cataloged indicators, no study contains all groups, and the ones that come closest are the studies of Rajak et al. [37] and Tafidis et al. [38], in which 77.55% and 79.59% of the indicator groups were identified, respectively. When analyzing from the perspective of the total groups and subgroups of indicators (total 89), 42.70% were identified in the study by Rajak et al. [37] and 43.82% in the study by Tafidis et al. [38].

In studies that used the pollution indicator group (AG), the main focuses of studies were the groups FC6 (32.19%), which analyzes the urban region, FC4 (17.81%), which presents the sustainability indicators, and FC7 (13.01%), which presents the consideration of the indicators through experts. Among the studies that used the AG (pollution) indicator group, none of these used the objective that analyzes the coverage of the transportation network (FC12).

Among the studies, 59 different analysis tools were identified, including AnTo_35 (hierarchical analysis of the process; AHP; 8.58%), AnTo_13 (descriptive and graphic statistical analysis; 7.09%), AnTo_12 (data enveloping analysis; DEA; 6.34%), and AnTo_33 (fuzzy logic; 6.34%). It is noteworthy that the multicriteria decision-making methods obtained a higher frequency (30.97%), having 15 distinct methods.

4. Discussion of Results

This section presents a summary of the extensive integrative literature review, showing the correlations made between the variables in this study (indicators, years, dimensions, study focus, and analysis tools) the perspectives of future studies on the evaluation of sustainability in land transportation.

After consolidating the results, some common points were identified, and some categories are indicated as priorities for a future research agenda. The following analyses are based on Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5 and Appendix D.

Only the indicators AT2 (trip distance), Y2 (financial evaluation: revenues), AU (traffic), M2 (modal diversity), A2 (accessibility of range), AS (security), and AG1 (air pollution) appeared in the four separation ranges of years (2005–2009, 2010–2013, 2014–2017, and 2018–2022). Some indicators that appeared only between 2018 and 2022 are as follows: O1 (effectiveness of the system), AF3 (monetary policy), AF4 (budget policy), AJ (social projects), AY1 (viability), R1 (environmental management), AW (added value), T4 (energy efficiency), and AL (environmental protection).

Some other observed highlights are that Y5 (infrastructure: exclusive bands) was the only unidentified indicator in studies between 2018 and 2022. AG1 (air pollution) is the most frequent indicator in the years 2018–2022, followed by AS (security; 2.28%), AG4 (noise pollution; 2.08%), A2 (accessibility of range; 2.08%), B (traffic accidents; 1.79%), AQ1 (transportation and infrastructure; 1.79%), A3 (tariff accessibility; 1.59%), AV (soil use; 1.59%), A1 (physical accessibility; 1.49%), H1 (energy consumption; 1.49%), and AD1 (mode occupation; 1.49%).

The analysis of indicators revealed higher study frequencies regarding the following: AG1 (air pollution; 6.98%), AS (security; 3.44%), A2 (accessibility of range; 3.49%), B (traffic accidents; 3.16%), A1 (physical accessibility; 3.21%), AG4 (noise pollution; 2.83%), A3 (tariff accessibility; 2.55%), M2 (modal diversity; 2.73%), H1 (energy consumption; 2.88%), and AV (soil use; 2.59%). In relation to the study focus, the following results were obtained (Figure 4):

(I)

Studies that contemplate AG1 (air pollution) are concentrated at 63.51% in the areas sustainability index (FC4), analyzes the urban region (FC6), and presents the classification of indicators (weights) through experts (FC7), and there are no studies regarding this indicator in the area analyzes the coverage of the transportation network (FC12).

(II)

Studies with AS (security) are concentrated at 65.75% in the areas sustainability index (FC4), analyzes the urban region (FC6), and the classification of indicators (weights) through experts (FC7), and there are no studies regarding this indicator in the areas with classification by type of transportation in relation to sustainability (FC9), the coverage of the transportation network (FC12), review the sustainability definitions (FC15), sustainability composite indicator (FC16), or focus on urban mobility (FC19).

(III)

Studies with A2 (accessibility of range) are concentrated at 68.92% in the areas sustainability index (FC4), analyzes the urban region (FC6), and the classification of indicators (weights) through experts (FC7), and there are no studies regarding this indicator in the areas with classification by type of transportation in relation to sustainability (FC9), focus on accessibility to public transportation (FC11), analyzes the coverage of the transportation network (FC12), more sustainable modes of transportation (FC13), sustainability composite indicator (FC16), and identifies the main studies on sustainable transportation (FC18).

(IV)

Indicator B (traffic accidents) is concentrated at 65.67% in the areas sustainability index (FC4), focusing on energy consumption (FC5), analyzes the urban region (FC6), and the classification of indicators (weights) through experts (FC7), and although focusing on energy consumption (FC5) has the lowest appearance, it demonstrates growth between 2018 and 2022; this indicator does not have studies in the areas accessibility to public transportation (FC11), analyzes the coverage of the transportation network (FC12), more sustainable modes of transportation (FC13), and identifies the main studies on sustainable transportation (FC18).

(V)

A1 (physical accessibility) concentrates 66.18% of its studies in the areas sustainability index (FC4), analyzes the urban region (FC6), the classification of indicators (weights) through experts (FC7), and focused on the emission of gases (FC8), and has no studies in the areas classification by type of transportation in relation to sustainability (FC9), analyzes the coverage of the transportation network (FC12), review the sustainability definitions (FC15), or presents sustainability composite indicator (FC16).

(VI)

AG4 concentrates 60.00% of its studies in the areas sustainability index (FC4), analyzes the urban region (FC6), and the classification of indicators (weights) through experts (FC7), and has no studies in the areas analyzes the coverage of the transportation network (FC12), evaluate perspective performance (FC14), or review the sustainability definitions (FC15).

(VII)

A3 (tariff accessibility) is concentrated at 85.19% in the areas sustainability index (FC4), focusing on energy consumption (FC5), analyzes the urban region (FC6), the classification of indicators (weights) through experts (FC7), and focused on the emission of gases (FC8), and has no studies in the areas with classification by type of transportation in relation to sustainability (FC9), application of different technologies (FC10), focus on accessibility to public transportation (FC11), analyzes the coverage of the transportation network (FC12), review the sustainability definitions (FC15), sustainability composite indicator (FC16), and identifies the main studies on sustainable transportation (FC18).

(VIII)

Indicator M2 (modal diversity) is concentrated at 77.59% in the areas sustainability index (FC4), analyzes the urban region (FC6), the classification of indicators (weights) through experts (FC7), and focused on the emission of gases (FC8), and has no studies in the areas with classification by type of transportation in relation to sustainability (FC9), focus on accessibility to public transportation (FC11), analyzes the coverage of the transportation network (FC12), evaluate perspective performance (FC14), or review the sustainability definitions (FC15).

(IX)

H1 (energy consumption) concentrates 63.93% of its studies in the areas in sustainability index (FC4), analyzes the urban region (FC6), and the classification of indicators (weights) through experts (FC7), and has no studies in the areas with classification by type of transportation in relation to sustainability (FC9), focus on accessibility to public transportation (FC11), analyzes the coverage of the transportation network (FC12), review the sustainability definitions (FC15), or sustainability composite indicator (FC16).

(X)

AV (soil use) concentrates 78.18% of its studies in the areas sustainability index (FC4), analyzes the urban region (FC6), the classification of indicators (weights) through experts (FC7), and focused on the emission of gases (FC8), and has no studies in the areas classification by type of transport in relation to sustainability (FC9), with focus on accessibility to public transportation (FC11), analyzes the coverage of the transportation network (FC12), review the sustainability definitions (FC15), and sustainability composite indicator (FC16).

The indicators AG1 (air pollution), AS (security), A2 (accessibility of range), and M2 (modal diversity) with the study focus FC6 (analyzes the urban region) appeared in all groups of years (2005–2009; 2010–2013; 2014–2017; and 2018–2022).

AG1 (air pollution) was the indicator most present in the sustainability dimensions accessibility, environmental, economic, energy, social, performance, resource, climate, system, technical, financial, and quality. The second most present indicator was H1 (energy consumption), being in the dimensions accessibility, environmental, economic, energy, social, performance, innovation, resource, activity, climate, system, and financial. The AJ (social projects) and Q (minimum transportation mode specifications) indicators appear only in the social dimension, and only the social dimension contemplates all indicators.

Environmental and social dimensions are present in all groups of years (2005–2009, 2010–2013, 2014–2017, and 2018–2022). The energy dimension was most frequent in studies between 2010–2013 and 2018–2022, and 9 of the 18 dimensions identified appeared only in studies of the years 2018–2022.

The environmental and social dimensions include all focuses of study. In the economic dimension, only review the sustainability definitions (FC15) was not identified in papers. The analyzes the urban region (FC6) focus did not show frequency in studies on activity, performance, innovation, and quality dimensions.

The sustainability index (FC4) and analyzes the urban region (FC6) focuses appeared in all groups of years. The focuses on the emission of gases (FC8) and application of different technologies (FC10) stand out in the 2018–2022 years for obtaining growth in the approach to studies near the main focuses of study. Finally, the focuses of study that appeared only in the years 2018–2022 were classification by type of transportation in relation to sustainability (FC9), focus on accessibility to public transportation (FC11), analyzes the coverage of the transportation network (FC12), more sustainable modes of transportation (FC13), sustainability composite indicator (FC16), and identifies the main studies on sustainable transportation (FC18). The analyzes the coverage of the transportation network (FC12) focus appeared the least in studies among all years.

The analyzes the urban region (FC6) focus is present in all indicators: AG1 (air pollution) was the most frequent indicator (in almost all study focuses) and was not found only in analyzes the coverage of the transportation network (FC12). The focus of study at a lower frequency was review the sustainability definitions (FC15), which contains the smallest number of indicators, only A2 (accessibility of range), AB (mobility), AG1 (air pollution), B (traffic accidents), and J (demand).

The FC6 (analyzes the urban region) study focus presents the largest number of analysis tools, highlighting the ANT_35 (hierarchical analysis method, AHP) tool, and did not present the analysis tools Anto_2 (comparative analysis of methodologies), Anto_17 (comparative performance evaluation), Anto_21 (BWM-D), Anto_30 (Malmquist index), Anto_31 (Java Space Model (JSM)), Ant_40 (SIR method), Anto_46 (transverse research), Anto_48 (Promethee), Anto_50 (logistics regression), Ant_56 (reliability tests), Ant_57 (non-parametric tests), and Anto_59 (TODIM). FC12 (analyzes the coverage of the transportation network) showed the lowest frequency, only appearing in the ANT_35 (hierarchical analysis method, AHP) analysis tool (Figure 5).

From the analyses and correlations between the variables, some points stand out:

(I)

The theme under research has been growing in proportion, especially in the years 2018–2022, appearing in 69.57% of the selected studies, demonstrating the importance of the theme but also reflecting that there are no methods or criteria established for the sustainability assessment of land transportation yet.

(II)

The most frequent study focus was FC6, analyzes an urban region, with 33.19% of studies largely appearing as an attempt to validate the proposed method.

(III)

The study focus less frequently appearing was FC12, analyzes the coverage of the transportation network, which may indicate the difficulty of researchers in proposing the evaluation of transportation as a whole due to the complexity of the theme of sustainability in land transportation.

(IV)

The three dimensions of sustainability that appear most frequently are those described as the Triple Bottom Line (economic, social, and environmental), with 87.84%. However, in addition to these 3 dimensions, 15 other dimensions categorized in this study were mapped. This may indicate that sustainability is beyond the three dimensions commonly used.

However, these 15 dimensions, according to specific contexts, can fit the description of the Triple Bottom Line. That being said, it is evident that even if these dimensions are categorized as groups, they have a greater prominence, which perhaps, as credited by the researchers, makes them more important for transportation and allows them to stand out in relation to the other identified ones.

(V)

The cataloged identification of 1202 different indicators demonstrates a lack of standardization of indicators regarding metrics and nomenclature, which is necessary to evaluate sustainability. In addition, many of these appear in their generic form, such as the identified indicator “accidents”. Thus, it is believed that these indicators should be more specific and standardized, as they are intended to be evaluated.

(VI)

The identification that none of the analyzed articles include all indicators may indicate a failure by researchers to compose their studies, not encompassing sustainability as a whole, which limits the results of sustainability assessments.

(VII)

The indicators that appear most in studies, AG (pollution) and A (accessibility), may be an indication that land transportation could have more impacts on sustainability through pollution and accessibility. However, the focus on these indicators can minimize or exclude indicators that are also relevant in sustainability assessments, as sustainability should add to the whole.

(VIII)

The indicator groups with fewer appearances in the studies (social projects (AJ), added value (AW), environmental certification (F), minimum transportation mode specifications (Q), cultural preservation (AI), environmental protection (AL), transportation worker social benefit (C), civil and human rights (N), and geographic space (P)) may indicate that researchers believe that these groups do not have a great impact or relevance on the sustainability of transportation and/or for the reason that these indicators are difficult to measure.

However, researchers should be cautious about the use of an indicator; as an example, indicator N (civil and human rights) appears to be a relevant item to achieve sustainability because it fits as a fundamental item of the social dimension of sustainability.

(IX)

Only the indicators AT2 (trip distance), Y2 (network density), AU (traffic), M2 (modal diversity), A2 (accessibility of range), AS (security), and AG1 (air pollution) appeared in the four separation ranges of years, which may indicate that these groups and subgroups are the main ones already established with agreement among researchers.

(X)

The indicators O1 (effectiveness of the system), AF3 (monetary policy), AF4 (budget policy), AJ (social projects), AY1 (viability), R1 (environmental management), AW (added value), T4 (energy efficiency), and AL (environmental protection), which appeared only in the years 2018–2022, may indicate that in recent years there has been a deepening of studies due to meeting sustainability as a whole.

(XI)

The AG1 (air pollution) indicator was most often measured in the years 2018–2022, more than any other indicator in any year, appearing to be an established and extremely important criterion for sustainability assessment.

(XII)

The classification of transportation that appears most in studies is willing in its generic form (Un2-transportation), and few studies have specificity regarding this, which could improve transportation evaluations as specifics have different characteristics.

(XIII)

The most commonly used analysis tool in studies is AHP (8.58%), which composes multicriteria decision support methods and appeared in 30.97% of studies, indicating that the multicriteria method is well accepted as a tool of analysis.

However, because the AHP method uses the criteria to be compared with each other, it could lead to inconsistency problems, given the large number of criteria (indicators) that appear for sustainability assessment.

Other multicriteria methods less used in studies, among others, are Electre, Promethee, Topsis, and BWM. These could make up for the lack of the AHP method in developing or selecting a larger number of criteria (indicators) for transportation assessment.

Another prominent point is that specific research has not been identified regarding the evaluation of rural transportation.

5. Conclusions

This study aimed to analyze the sustainability assessment indicators in land transportation in order to present the current situation and prospects for future studies.

The analysis of an integrative bibliographic review in relation to a large number of published works was used. Among the evaluations made there are study focuses, indicators, year of publication, sustainability dimensions, analysis tools, and so on. The main results of this research pointed out the results given below.

There has been growth in the theme of sustainability indicators in land transportation in recent years, and 53% of papers were published in 2020–2022.

Although 88.68% of studies are focused on the social, environmental, and economic scope, many have other dimensions because they attribute differentiated importance, such as climate, quality, and legal innovation.

The main study objectives are related to analyzing an urban region; the proposition and weighting of sustainability indicators; the analysis of interactions between sustainability indicators; energy consumption; and governmental and political issues.

The most commonly identified indicators are related to pollution, accessibility, energy consumption, fuel and natural resources, infrastructure, satisfaction and quality, availability and diversity of transportation, safety, environmental impact, occupation and capacity of the transportation mode, accidents in transit, and air pollution.

Most of the analysis tools are concentrated in multicriteria decision support methods and statistical methods.

Some common points have been identified in papers, and some categories are indicated as priorities for a future research agenda: the lack of standardization of indicators regarding metrics and nomenclature to assess sustainability and the lack of studies covering sustainability as a whole, which limit the results of sustainability assessments.

Deficiencies in relation to indicators include social inclusion, political–legal issues, and civil/human rights, in addition to the standardization of indicators in specific sectors, since each sector has its own specificity: for example, the standardization of indicators to evaluate public schools, agricultural cargo, containers, taxis, etc.

Another indicator that can make it difficult to assess the sustainability of transportation is how the sustainability dimensions are separated. A solution could be the resizing of the traditional dimensions to include others, such as innovation, performance, public policies, social inclusion, resources, technicians, etc. This can assist researchers and sector managers in proposing forms of sustainability assessment in transportation more efficiently.

Finally, it is emphasized that most studies give importance to data availability to compose indicators, i.e., the barriers to availability and data access. However, if this is a mistake, if a group or category of indicator does not have data availability, would it be discarded from the evaluation? Sustainability assessment should cover the whole, regardless of the difficulty of evaluating. This is a barrier for research in this sector, generating the need for discussion for a solution.

Thus, this study contributes to the academic community, government managers, and society by pointing out a vast bibliographical study on the indicators used to evaluate sustainability in land transportation from various perspectives and research contexts.