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Article

Conceptual and Methodological Perspectives of Travel Time in an Integrated Passenger Transport System

by
Borna Abramović
1,* and
Milan Živković
2
1
Faculty of Transport and Traffic Sciences, University of Zagreb, 10000 Zagreb, Croatia
2
Zagreb Area Integrated Transport LLC, 10000 Zagreb, Croatia
*
Author to whom correspondence should be addressed.
Sustainability 2026, 18(10), 5036; https://doi.org/10.3390/su18105036 (registering DOI)
Submission received: 8 April 2026 / Revised: 24 April 2026 / Accepted: 14 May 2026 / Published: 16 May 2026
(This article belongs to the Special Issue Exploratory Railway Track Structure, Railway Operation and Transport in Sustainable Development of Railway Systems)
Versions Notes

Abstract

Sustainable transport management (STM) has become an increasingly important issue in recent years, as cities have faced growing traffic congestion, air pollution, and other transport-related challenges. Travel time (TT) represents one of the critical determinants of Quality of Service (QoS) and user satisfaction in public passenger transport (PPT). TT extends beyond in-vehicle duration and encompasses a sequence of temporal components, including access, waiting, transfer, and egress times. TT reflects the complexity of an integrated passenger transport system (IPTS), where users experience transport services as a door-to-door journey rather than isolated trips. This article analyses the TT within IPTSs through the lens of European quality standards EN 13816 and EN 15140 for PPT. Standard EN 13816 provides a normative framework for defining TT as a key QoS criterion reflecting user expectations and a user-oriented perspective, while standard EN 15140 operationalises this framework by specifying methodological requirements for the measurement and evaluation of the delivered TT quality at system-level performance objectives. This research highlights a structural gap between the conceptualisation of TT as a door-to-door journey, a user-oriented phenomenon, and its measurement through fragmented, mode-specific performance metrics. It limits the ability of transport authorities and operators to accurately evaluate the QoS and to design efficient urban mobility (UM) systems.

1. Introduction

According to projections from the United Nations, 68% of the world’s population is expected to live in urban areas by 2050, up from 55% in 2018 [1]. This rapid urban migration, with roughly 2.5 billion more people living in cities, presents a significant burden on environmental management, infrastructure, and public services. Creating sustainable and efficient UM solutions is crucial for addressing the challenges of modern cities and ensuring a high quality of life for their residents. STM is the planning and implementation of mobility systems that minimise environmental impact while remaining economically viable and socially equitable. It involves multiple strategies, including the adoption of low-emission vehicles, integration of transport modes, optimisation of routes and schedules, and implementation of supportive policies. These measures aim to reduce emissions, improve service efficiency, and enhance accessibility [2]. Sustainability is not solely about environmental performance. A transport system must also be attractive and competitive to users. This is where operational factors, particularly TT, become crucial. Without a competitive TT, even the most environmentally friendly transport systems may fail to attract potential users.
In classical transport theory, TT is regarded as a fundamental operational variable, representing the temporal cost associated with moving between two points in a transport network. It is intrinsically linked to the concepts of generalised cost, the value of time, and overall network performance, serving both as a measure of system efficiency and as a key determinant of passenger route choice and modal selection [3]. TT is widely recognised as one of the most critical determinants of transport system performance and travel behaviour. It is not merely a technical measure of movement duration but a composite indicator that reflects system efficiency, reliability, punctuality, and overall user experience [4].
Research [5] has highlighted that TT should be decomposed into several interrelated components, such as (1) access time, (2) waiting time, (3) in-vehicle time, (4) transfer time, and (5) egress time, especially for PPT, where passenger journeys are shaped by complex temporal interactions among transport modes, timetables, and infrastructure [6]. Consequently, TT serves not only as an operational parameter but as a key criterion of QoS and system integration.
Standard EN 13816 [4] defines QoS in PPT as the degree to which a transport service satisfies user expectations and requirements. The standard introduces a comprehensive quality model structured around the following eight main criteria [4]: (1) availability; (2) accessibility; (3) information; (4) time; (5) customer care; (6) comfort; (7) safety and security; and (8) environmental impact. Within this framework, time is defined as a core quality criterion encompassing length of trip time, punctuality, and reliability. The standard adopts a user-oriented perspective, recognising that passengers evaluate transport services based on the total duration and temporal structure of their journeys.
Standard EN 15140 [6] complements standard EN 13816 by specifying the requirements and recommendations for systems that measure the delivered QoS in PPT. While standard EN 13816 defines what should be measured, standard EN 15140 focuses on how it should be measured. The standard provides guidance on the design and implementation of measurement systems, including data collection methods, sampling strategies, validation procedures, and reporting mechanisms, ensuring that service quality assessment is systematic, reliable, and comparable across networks and operators [7].
In the context of IPTSs, standard EN 13816 plays a strategic role by providing the common terminology and conceptual structure for the QoS across various modes and operators, while standard EN 15140 ensures that the quality measurement processes are consistent, reliable, and transparent across different operators and modes. This is essential for achieving objective and comparable performance assessments in complex networks.

2. Literature Review

Sustainable transport has become a central topic in transport planning due to increasing concerns about climate change, congestion, and efficient UM. PPT systems are widely recognised as a key pillar of sustainable urban development because they reduce emissions, improve accessibility and efficiency, and optimise resource use. European cities have started to reorganise their UM systems based on a strategic plan designed to satisfy the mobility needs of city residents for a better quality of life. The Sustainable Urban Mobility Plan (SUMP) has been designed to solve transport problems in urban areas more efficiently.
Public transport services refer to the transport systems that are available for use by the public. PPT can be defined as transport available for public use, a transport system (of buses, trains, etc.) that runs on fixed routes at set times [8]. PPT is an important component of UM and is frequently used by people to commute to work or travel within a city or region. It can be used by anyone with a valid ticket or a pass to the inhabitants of a town, city, or even a region. It can also vary in its diversity. The advantages of PPT systems are numerous; they help ease traffic congestion, reduce air pollution, support sustainable mobility, and enhance access to employment, education, and healthcare services.
TT is a central concept in transport studies and is widely used as a key criterion for evaluating the performance, attractiveness, and efficiency of PPT systems. Traditionally, TT has been treated as a single, aggregate measure representing the duration of a journey between an origin and a destination point. However, extensive research has demonstrated that TT is inherently multidimensional, comprising several distinct components that are perceived and valued different by users [9]. TT is a useful tool for assessing both the user experience of taken journeys and the overall QoS provided by a particular network route or the whole PPT system.
Within this context, TT is a critical performance indicator influencing both system efficiency and user satisfaction. It directly affects modal choice, competitiveness with private vehicles, and overall sustainability outcomes.

2.1. Concept and Multidimensionality

In the public transport literature, TT is commonly defined as the total door-to-door journey time, encompassing all stages of a passenger’s trip rather than only the in-vehicle portion. This comprehensive definition reflects the actual experience of PPT users and provides a more accurate basis for a QoS evaluation and policy analysis [10]. The concept extends beyond the operational TT to include elements that are external to vehicle movement but essential to user experience, such as access, waiting, and egress time. TT is a critical, dynamic component in transport planning that affects mode choice, travel behaviour, and overall PPT performance.
Recognising TT as a multidimensional construct has important implications for transport modelling. It challenges the adequacy of using the average in-vehicle travel time alone as a performance metric and highlights the need for comprehensive door-to-door assessments. Furthermore, it supports the differentiated weighting of the TT components in demand modelling and cost–benefit analysis (CBA), often reflected through the use of specific TT values [11]. This multidimensional approach also underscores the importance of service design strategies aimed at reducing not only total travel time (TTT) but the most burdensome components, such as waiting and transfers. Improvements in service frequency, timetable coordination, and first-/last-mile connectivity can therefore yield substantial gains in the perceived QoS even when the in-vehicle TT remains unchanged [12].

2.2. Punctuality, Regularity and Reliability of Service

PPT systems are evaluated not only by speed and cost but by their punctuality, regularity, and reliability of service. These attributes strongly affect travel behaviour, system efficiency, and the competitiveness of PPT relative to private modes.
Punctuality refers to the degree to which public transport vehicles depart or arrive within a predefined time window correlated to the timetable. It is typically expressed as the percentage of services arriving or departing on time. Punctuality is a key criterion of the QoS in PPT and a critical determinant of system efficiency, user satisfaction, and economic performance. Historically, transport planning has focused on reducing the average TT and increasing capacity. However, the empirical evidence has shown that passengers value punctuality highly, often as much as speed or cost [13]. Transport economics quantifies these effects through the concept of the value of time and the value of reliability, which include penalties for lateness. Studies [14] have shown that PPT users perceive lateness as more burdensome than equivalent increases in average travel time.
Regularity of service is a central performance QoS criteria in PPT systems, reflecting the consistency with which vehicles adhere to planned schedules. Unlike punctuality, which evaluates deviation from scheduled times at specific control points, regularity captures the stability and evenness of service delivery over time. Regularity directly influences passenger waiting time, vehicle occupancy distribution, and overall network efficiency [15]. Poor regularity often manifests as vehicle bunching, uneven load distribution, and service gaps, thereby reducing system capacity and user satisfaction [16]. Maintaining regularity and consistent TTs are the key attributes of reliable PPT services [17]. The effective management of regularity requires a combination of robust scheduling, real-time operational control, infrastructure support, and data-driven monitoring systems [18]. It depends on simulating the network demand variation over the analysis time horizon to examine a set of pre-generated paths [19]. As PPT systems evolve towards higher frequencies and automation, maintaining regularity will remain central to enhancing both operational efficiency and user satisfaction.
Reliability has a great influence on the user’s QoS perception. Travel time reliability (TTR) is defined as a measure of the expected range in TT, providing a quantitative indicator of predictability. TTR refers to the consistency and predictability of travel durations on transport networks and is linked to the consistency of service performance. The reliability of the PPT system is often defined as one minus the probability of failure [20,21]. Another definition of reliability defines it as “The transport system’s certainty and predictability in travel times is a crucial aspect to consider” [22]. Reliability is linked to the consistency of service performance. Empirical studies [23] have demonstrated that passengers value reliability and predictability, often preferring slightly longer but more reliable journeys over shorter but uncertain ones. Travel time variability (TTV) is a crucial indicator of PPT network performance, assessing the TTR and delays. TTV has several distinct components, including differences in the TT from day-to-day, over the course of the day, and even from vehicle-to-vehicle [24]. TTV measures the reliability of service. It quantifies the uncertainty in TT for a given route over a specific period, reflecting any unexpected delays caused by factors such as short-term incidents (e.g., vehicle breakdowns), long-term issues (e.g., work zones, route closures) or random events (e.g., accidents, travel demand fluctuations) [9,25]. Analysing TTV, it serves several purposes, such as proactively managing congestion, identifying optimal routes for PPT services, optimising schedules, and developing traffic management strategies in PPT [22].
Moreover, the regularity and reliability of the trip can significantly affect stress levels and user satisfaction, which are associated with additional trip characteristics, such as trip directness, the number of transfers, proximity to stops and stations, and waiting times [26]. However, these results can vary depending on a combination of traveller characteristics and attitudes, with gender, age, and income often playing a key role [27]. Users value reliability often as much as speed, so reducing the TTV is a vital target in modern transport systems.

2.3. Perception and Behaviour

TT perception plays a critical role in shaping travel behaviour and influencing the attractiveness of PPT. While TT is often measured objectively in minutes, a substantial body of the literature [28] has demonstrated that passengers perceive TT subjectively, and these perceptions frequently diverge from actual travel durations. For example, reliable services and accurate real-time information have been shown to decrease the perceived waiting time even when the actual time remains constant, thereby increasing user satisfaction and loyalty [29]. Users of PPT have potentially more opportunity to use their TT for personal activities, since they are not preoccupied with operating a vehicle. User and trip characteristics (e.g., transport mode, trip purpose and duration, attitudes and preferences) could influence the relationships between experience factors, travel activities, and user satisfaction. For example, user satisfaction on any transport mode decreases as the travel duration increases, although this relationship appears not to be linear, with satisfaction peaking at around 10 min and significantly dropping beyond 30 min [30].
Behavioural weighting in PPT refers to the incorporation of user perceptions and cognitive biases into transport frameworks and evaluations. Conventional approaches assume there is rational decision-making based on objective measures, such as travel time and cost. Research in transport psychology and behavioural economics [31] has indicated that passengers do not experience TT uniformly across different journey stages. Time spent waiting, transferring, or walking is generally perceived as more onerous than time spent in-vehicle, even when the objective duration is identical. Studies [29] have shown that waiting time can be perceived as up to two or three times longer than in-vehicle time, particularly when service reliability is low or information provision is deficient. The incorporation of behavioural weighting aligns with developments in discrete choice theory, which allows for the probabilistic representation of individual preferences [32]. This integration allows for a probabilistic representation of individual preferences, capturing how individuals evaluate, prioritise, and trade off different attributes, rather than assuming perfectly rational, consistent choices. Consequently, the perceived TT often exerts a stronger influence on travel behaviour than the actual TT, especially in the context of PPT.

2.4. Sustainable Urban Mobility

The concept of sustainable UM has its roots in the definition of sustainability. According to a widely accepted definition, sustainability is development that meets the present needs without compromising the ability of future generations to meet their needs [31]. In their article [33], Kennedy et al. described the four pillars of sustainable urban transport, which include the following: (1) effective land use and sustainable management; (2) fair and efficient financing; (3) strategic investment in infrastructure; and (4) attention to the design of surroundings. In [34], Kenworthy discussed a conceptual UM model. Kenworthy’s model highlights the connection between UM and the shape of an urban area. He proposed the introduction of better PPT systems and conditions for non-motorised means, with some minimal increase in road capacity. Two other studies cover sustainable performance indicators and analytical approaches, which describe the efficiency of sustainable urban transport and the sustainable transport system performance evaluation [35,36].
There are also several studies on transport system indicators. Study [37] focused on developing indicators for sustainable transport planning, while [38] proposed an evaluative and logical approach to compiling sustainable transport indicators. The results of [39] indicated how these findings could be used to achieve the network planning of intermodal transit systems in real cities to achieve comprehensive results from services existing in cities of different sizes.

2.5. Value of Travel Time and Travel Time Savings

The value of travel time (VTT) and value of travel time savings (VTTS) are fundamental concepts in transport economics and STM. They are widely used to evaluate transport policies, infrastructure investments, and service improvements. In the context of PPT, these concepts help quantify the benefits of reducing TT and improving service efficiency. Weighting factors are used to convert the different components of TT into a common generalised cost. Empirical research [13,40] has consistently shows that passengers perceive walking (1.5 to 2.0), waiting (2.0 to 3.0), and transfer time (2.5 to 4.0 or the equivalent of 5 to 15 min) as more onerous than in-vehicle time (baseline value of 1.0), leading to systematic weighting differences. Understanding how users perceive and value time is essential for designing transport systems that are both efficient and attractive, thereby supporting broader sustainability goals.
The VTT represents the opportunity cost of time spent travelling. Empirical studies [30] have shown that the VTT is not uniform, but varies significantly based on income, trip purpose, and transport modes, with private vehicle users often exhibiting higher values than PPT users. It reflects the amount of money and time a user would be willing to pay to avoid spending additional time on a journey, assuming all other attributes remain constant. The VTT, defined as the willingness to pay for TT savings, tends to be higher for users during weekdays, and varies with comfort, reliability, and the ability to work while travelling [41].
The VTTS refers to the monetary value individuals assign to a reduction in TT. It is a dominant component in the CBA of transport projects. It serves as a primary justification for investments in infrastructure and service improvements. However, studies [42] have suggested that the VTTS is typically estimated using stated- or revealed-preference methods that assume a willingness to pay for faster travel options.

2.6. Research Gap

The identification of research gaps was based on a structured review of the academic literature on TT, PPT, and IPTSs. Relevant studies were identified using major academic databases, including Scopus, Web of Science, and Google Scholar. Search queries combined key terms, such as TT, PPT, IPTS, multimodal transport, values of TT, time-weighted averages, and accessibility. Boolean operators were used to refine the results (e.g., “travel time” AND “multimodal” AND “accessibility”).
Despite the central role of TT in IPTSs, the existing research remains fragmented across methodological, spatial, and conceptual dimensions. Current approaches rely heavily on static, aggregate measures, and often fail to capture the dynamic, multimodal, and behavioural nature of door-to-door journeys. Consequently, there is a clear research gap in developing unified, behaviourally informed, and temporally dynamic models of TT that more accurately reflect the complexity of IPTSs. For example, accessibility studies often sum walking, waiting, and in-vehicle time into a single metric without behavioural weighting or interaction effects.
Due to the insufficient development of a behaviourally weighted integrated TT framework that captures multimodal user experience in an IPTS, this article will attempt to provide an answer to this understudied area.

3. Conceptualisation of Travel Time in Public Passenger Transport

Public passenger transport contributes to urban and regional development by providing mobility, supporting economic activity, and promoting social inclusion. Among the various factors affecting transport system performance, TT stands out as a fundamental indicator of efficiency and user satisfaction. TT influences modal choice, accessibility, and productivity, making it a central focus of economic policy in transport planning [42].

3.1. Travel Time as a QoS Criteria

PPT systems are increasingly evaluated not only on operational efficiency but on the delivered QoS to users. QoS influences ridership levels, modal choice, and public acceptance of transport policies. TT is consistently identified as one of the most important determinants of the perceived QoS and user satisfaction [43].
Standard EN 13816 establishes a normative framework for defining, structuring, and targeting the QoS in PPT. Within this framework, TT is situated in the broader “time” QoS criteria alongside punctuality, regularity, and reliability of service. Rather than prescribing a singular technical definition, the standard conceptualises TT as a composite criterion in PPT, reflecting both the technical performance of transport systems and the experienced QoS perceived by users [44]. Standard EN 13816 operates primarily at the conceptual and normative level. It defines what constitutes TT from a QoS perspective but does not prescribe detailed measurement methodologies. This normative role allows the standard to serve as a universal conceptual framework applicable to diverse transport systems and organisational contexts.

3.2. Multidimensional Formulation

A distinctive feature of standard EN 13816 is its explicit integration of user perception into the definition of the QoS criteria. A multidimensional formulation of TT in PPT decomposes the total door-to-door journey into distinct, quantifiable components to better reflect user experience and system performance, each of which contributes differently to the perceived QoS.
The core dimensions of multimodal TT are as follows [5]:
  • Access time—time required to reach the first stop or station from the origin point;
  • Waiting time—time spent waiting for the departure of the first vehicle;
  • In-Vehicle time—time spent travelling within vehicles;
  • Transfer time—time required to change vehicles or modes, including walking and waiting within interchange nodes;
  • Egress time—time required to reach the destination point from the last stop or station.
These components reflect the holistic nature of TT as conceptualised in standard EN 13816, which emphasises the passenger journey as an integrated process rather than a sequence of isolated operations.

3.3. User-Oriented Perspective

One of the major challenges in PPT planning is determining the complexity of the variables involved in the user’s travel choices. Usually, individuals make decisions to maximise their utility. Regarding the travel mode choice and the users’ satisfaction with travel, the perceived value plays a significant role in the user’s decision [45]. It does not always rely on the purpose of the journey.
As such, the users’ perception of the VTT can impact the level of satisfaction, which varies across different transport modes based on the perceived QoS in different situations. However, the users’ satisfaction can be influenced by different events experienced while on the journey. For instance, previous studies [46] have shown a discrepancy between the PPT users’ travel experience and their preferences, and attitudes towards PPT modes most likely impact on their QoS evaluation of the PPT service and their level of satisfaction.

4. Methodological Perspective of Travel Time in Public Passenger Transport

Standard EN 15140 is a European quality standard that defines the basic requirements and practical recommendations for systems used to measure the delivered QoS in PPT. It was published under CEN (European Committee for Standardization) in 2006 as EN 15140:2006 and is still recognised in national implementations of the CEN standard [6]. Standard EN 15140 focuses on how the QoS should be measured in PPT. In the context of TT, the standard defines the methodological principles for data collection, measurement, and evaluation. The standard also recognises the importance of multiple data sources, including automated vehicle location systems, ticketing data, passenger surveys, and manual observations.

4.1. Performance Indicator of Travel Time

The standard introduces a systematic approach to the measurement of QoS, including the definition of reference points, data sources, sampling strategies, and statistical evaluation methods. In the case of TT, standard EN 15140 distinguishes between planned and actual TT, thereby enabling the assessment of reliability and punctuality as derived indicators [47]. Unlike standard EN 13816, standard EN 15140 is based on an objective measurement methodology. By converting abstract quality features into empirically observable indicators, it establishes standards and recommendations for systems that measure the delivered QoS. In this context, TT is considered to be an operational variable that is systematically measured, verified, and reported.
As a result, TT is redefined by standard EN 15140 from an abstract QoS criteria to a quantifiable performance indicator that is integrated into monitoring systems. This shift reflects the increasing emphasis on evidence-based governance and accountability in PPT.

4.2. Methodological Framework

From a methodological perspective, standard EN 15140 can be understood as an operational model of the QoS measurement. It bridges the gap between abstract quality concepts and empirical data by defining a logical framework for data collection and analysis. In this sense, standard EN 15140 embodies the principles of systems engineering and performance management applied to PPT. While standard EN 13816 defines the meaning and structure of TT, standard EN 15140 specifies how this indicator should be operationalised within the QoS measurement systems, as follows [48]:
  • Design of the measurement system—balance between the customers’ viewpoint and use of the measurement as a management tool for reaching the targeted QoS;
  • Conduct of measurement—measurement shall be performed during operating hours, and data collection and data processing shall be transparent, traceable, and verifiable;
  • Specific requirements—measurements can be made by surveys or by technical means, and they can be continuous or by sample.

4.3. Instrumental Rationality

Instrumental rationality is a mode of thought focused on identifying and implementing the most efficient, economical, and effective means to achieve a predefined end or goal. It is essentially a “means-to-an-end” approach, concentrating on how to achieve a goal rather than why that goal is pursued [49]. In PPT, instrumental rationality means organising systems to achieve the defined QoS (efficiency, punctuality, safety, etc.) using the most effective and measurable method.
The conceptual logic of standard EN 15140 is fundamentally instrumental. A key contribution is the distinction between planned and actual TT. The planned TT refers to the duration specified in timetables, while the actual TT reflects real operational conditions. The deviation between these two measures provides a basis for evaluating reliability and punctuality. This operationalisation reflects a rationality where the QoS is made understandable via quantitative measurement.

5. Comparative Analysis: Conceptual vs. Methodological Dimensions of Travel Time

Standard EN 13816 defines the time criterion as a core QoS criteria that implicitly includes TT, punctuality, regularity, and reliability of service, but it does not prescribe a specific formula or value. Rather, it forms a category that users of the standard must specify and measure. Standard EN 15140 does not define the specific criteria itself (time, punctuality, etc.). Instead, it focuses on how to build a measurement system to measure the criteria defined in standard EN 13816.
Below is Table 1 showing a side-by-side comparison of the TT criteria for the analysed European standards.
The relationship between standards EN 13816 and EN 15140 reflects a fundamental distinction between conceptualisation and measurement in QoS management. Standard EN 13816 defines TT as a composite, user-oriented quality criteria embedded in a broader normative framework of the QoS. By contrast, standard EN 15140 operationalises this indicator through technical and statistical methodologies.
Table 2 shows a comparison of standards EN 13816 vs. EN 15140 focused on their role in PPT systems.
The relationship between standards EN 13816 and EN 15140 can be conceptualised as a dual-layer model. Standard EN 13816 provides the conceptual framework for the QoS, whereas standard EN 15140 operationalises this framework through structured measurement methodologies. Conceptual frameworks define what should be measured, including components such as waiting time and service quality. Methodological approaches provide tools to measure, quantify, and analyse these components.

6. Travel Time in Integrated Passenger Transport System

The combined application of standards EN 13816 and EN 15140 has important implications for the design and evaluation of IPTSs. By integrating conceptual definitions with measurement methodologies, the standards successfully enable a systematic approach to the QoS management.

6.1. Integrated Approach of Travel Time

Building on the theoretical and standardisation-based analysis presented in previous chapters of this article, the TT in PPT can be synthesised as a dual-layer structure in transport, where the QoS is conceptualised at the normative level and subsequently operationalised through empirical metrics. This distinction is particularly significant in IPTSs, where the TT emerges from interactions between various transport modes, infrastructure, operations, information systems, and passenger behaviour.
From a theoretical perspective, the European standards reflect the dual role of TT as both a behavioural and operational variable. Standard EN 13816 captures the behavioural dimension by emphasising user perception, while standard EN 15140 operationalises the technical dimension through measurable indicators. Furthermore, the standards collectively support a shift from a mode-specific evaluation towards a system-level assessment. By conceptualising TT as an integrated indicator and providing tools for its measurement, standards EN 13816 and EN 15140 enable a holistic evaluation of multimodal door-to-door journeys. European standard EN 13816 facilitates the identification of critical components influencing user satisfaction, such as waiting and transfer times, which are often disproportionately weighted in the user’s perception.
The integrated approach to the TT analysis represents a shift from fragmented performance indicators to a holistic evaluation of the passenger journey. By combining objective and perceived time components with reliability and multimodal integration, the framework provides a comprehensive basis for analysing IPTSs.

6.2. Integrated Travel Time Framework

The integrated travel time framework (ITTF) shifts transport from how fast users can reach their destinations to how they perceive the TT within the whole IPTS. A new approach within the context of standards EN 13816 and EN 15140 aims to move beyond the traditional time measurement and instead evaluate the user-perceived performance of the door-to-door journey in IPTSs. The ITTF builds on this paradigm by treating the journey as a sequence of interconnected stages, each contributing differently to the perceived TT. It provides a comprehensive and behaviourally based approach to evaluating IPTSs. By recognising that not all TT is perceived equally, the framework enables more effective planning, better resource allocation, and improved user satisfaction and experience.
Equation (1) shows the mathematical formulation of the ITTF used in mobility and transport systems. The framework uses weighted time components as follows:
TITTF = Taωa + Twωw + Tiωi + Ttωt + Teωe
where the notations above are explained as follows:
  • Ta is the access time;
  • Tw is the waiting time;
  • Ti is the in-vehicle time;
  • Tt is the transfer time;
  • Te is the egress time;
  • ω is the perceived weight associated with each time component.
Equation (1) represents a conceptual model of the ITTF, illustrating the decomposition of a passenger journey into sequential stages and the integration of multiple time-related indicators into a unified analytical structure. It represents the door-to-door journey, consisting of origin, waiting, in-vehicle travel, transfer, egress, and destination, emphasising that the TT is experienced as a continuous process rather than as isolated segments. Overall, this mathematical formulation illustrates the transition from a traditional, system-based TT measurement towards a holistic, user-centred evaluation framework, consistent with the QoS criteria of standard EN 13816 and the user’s perceived disutility weight. Typical empirical values suggest the following:
  • Tw > Ti—waiting is more onerous than travelling;
  • Tt—highest value due to disruption and uncertainty;
  • Ta, Te—depend on urban structure and infrastructure quality.
The weighting structure reflects the user’s perception of the TT rather than the objective TT. Waiting time, often experienced under uncertain or uncomfortable conditions, carries greater psychological value. Similarly, transfers introduce burdens, particularly in poorly designed integrated transport systems.

6.3. Empirical Estimation of the ITTF

The empirically estimated ITTF is particularly useful for evaluating multimodal systems, where first- and last-mile connectivity play a critical role. Integrating walking, cycling, and micro-mobility options into the IPTS network can significantly reduce access, waiting, in-vehicle, and egress times in the door-to-door journey. The approach is grounded in discrete choice theory, where behavioural preferences are inferred from the observed or stated travel decisions and translated into time-equivalent weights.
The following Table 3 is an OD (origin–destination) comparison of the weighted and unweighted TTs.
The results show how the ITTF changes the perceived TT in practice. The comparison between the unweighted and weighted OD TT demonstrates that treating all minutes of a door-to-door journey as equivalent leads to a systematic misrepresentation of the perceived and objective TT. The OD pair A–C becomes much higher because of long waiting and transfer times, which applies a disproportionately large influence on the perceived TT; whereas the car-based OD relations A–D remain largely unaffected due to the absence of transfer components.
As a result, the OD pairs involving PPT, especially those with long waiting times or transfers, experience a substantial increase in the perceived TT relative to their objective values, whereas the car-based OD relations remain largely unaffected due to the absence of transfer components.

7. Conclusions

Travel time represents one of the most fundamental variables in PPT planning, analysis, and evaluation. It directly affects user satisfaction, accessibility, system performance, operational efficiency, and the overall attractiveness of PPT systems. Traditionally, TT has been viewed as a simple measurable quantity representing the duration of movement between two points. However, transport research recognises TT as a multidimensional construct that includes behavioural, psychological, economic, and operational aspects. PPT systems must not only be environmentally friendly but time-competitive with private vehicles. Integrating TT considerations into transport planning and management is therefore essential for creating efficient, inclusive, and sustainable mobility systems.
This research has demonstrated that TT occupies a structurally different position within the EN 13816 and EN 15140 standards. Standard EN 13816 provides the conceptual framework for the QoS, whereas standard EN 15140 operationalises this framework through structured measurement methodologies. Together, they form an integrated quality management system in which the quality objectives defined under standard EN 13816 are monitored and evaluated using the measurement systems designed in accordance with standard EN 15140.
In an IPTS, standard EN 13816 harmonises the quality concepts across various transport modes, while standard EN 15140 ensures the objective and comparable performance measurement. Together, they form a complete quality management system for PPT and IPTSs. Standard EN 13816 defines what TT means as a quality indicator in PPT, while standard EN 15140 defines how that TT must be measured, calculated, and validated in practice.
This article demonstrates that weighting factors in integrated travel time models are a critical component of an accessibility analysis. They are grounded in behavioural theory and empirically estimated using discrete choice models and stated preference methods. By assigning higher disutility to walking, waiting, and transfer times relative to in-vehicle travel, these weights ensure that accessibility measures reflect user experiences. Such extensions would preserve the normative coherence of standards EN 13816 and EN 15140, while enhancing their explanatory power and passenger relevance in contemporary IPTSs.
Standard compliance alone does not ensure QoS alignment. An integrated, data-driven, and system-oriented extension of the European quality standards is necessary to enhance the QoS in PPT and especially in IPTSs. Future research should aim to extend the mentioned European standards to obtain QoS through a behaviourally weighted TT valuation and integrated door-to-door and multimodal journeys.
This dual-standard approach facilitates coordinated governance, enhances transparency, and supports evidence-based decision-making in transport planning and management. From a systemic perspective, the integration of standards EN 13816 and EN 15140 enhances the ability of transport systems to respond to user needs, to improve the QoS reliability, and to promote sustainable mobility. Their joint implementation can therefore be regarded as a fundamental pillar of quality-oriented management in IPTSs.

Author Contributions

Conceptualisation, M.Ž. and B.A.; methodology, M.Ž.; validation, M.Ž. and B.A.; formal analysis M.Ž. and B.A.; resources, M.Ž.; data curation, M.Ž. and B.A.; writing—original draft preparation, M.Ž.; writing—review and editing, M.Ž. and B.A.; visualisation, M.Ž.; supervision, B.A.; project administration, M.Ž. and B.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analysed in this study.

Conflicts of Interest

Author Milan Živković is employed by the company Zagreb Area Integrated Transport LLC. The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Table 1. TT criteria in PPT system.
Table 1. TT criteria in PPT system.
CriteriaEN 13816EN 15140
waiting timeperceived quality factorobservation or data-based measurement procedures
transfer timemultimodal quality factormeasure intermodal connections and transfer reliability
total journey timekey quality criteria reflecting user experiencemeasuring methods and data integration
punctualitycompliance with timetable expectationscalculation methods, thresholds, and sampling rules
reliabilitystability and predictability of TTstatistical methods to assess variability and robustness
regularityequality of service intervalsoperational metrics and validation procedures
Table 2. Side-by-Side Comparison of Standards EN 13816 and EN 15140 for travel time criteria in PPT.
Table 2. Side-by-Side Comparison of Standards EN 13816 and EN 15140 for travel time criteria in PPT.
AspectConceptualMethodological
standardEN 13816 EN 15140
scopeQoS criteriameasurement system design
focusservice quality frameworkmeasurement framework
perspectiveuser-orientedsystem-oriented, operational
indicatorwhat to measurehow to measure
componentsaccess, waiting, in-vehicle, transfer, egress timeGPS data, surveys, simulation, timetable analysis
measurement methodindicativeprescriptive, structured
applicationtransport and policy theoryplanning and evaluation
Table 3. TT in IPTS and the ITTF concept.
Table 3. TT in IPTS and the ITTF concept.
OD PairTT ComponentTime (min)Weight ValueIPTS (min)ITTF (min)
A–BTa2.51.531.040.5
Tw4.02.0
Ti20.01.0
Tt2.02.5
Te2.51.5
A–CTa3.01.548.065.0
Tw8.02.0
Ti30.01.0
Tt4.02.5
Te3.01.5
A–DTa1.51.539.041.5
Tw1.02.0
Ti35.01.0
Tt0.02.5
Te1.51.5
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Abramović, B.; Živković, M. Conceptual and Methodological Perspectives of Travel Time in an Integrated Passenger Transport System. Sustainability 2026, 18, 5036. https://doi.org/10.3390/su18105036

AMA Style

Abramović B, Živković M. Conceptual and Methodological Perspectives of Travel Time in an Integrated Passenger Transport System. Sustainability. 2026; 18(10):5036. https://doi.org/10.3390/su18105036

Chicago/Turabian Style

Abramović, Borna, and Milan Živković. 2026. "Conceptual and Methodological Perspectives of Travel Time in an Integrated Passenger Transport System" Sustainability 18, no. 10: 5036. https://doi.org/10.3390/su18105036

APA Style

Abramović, B., & Živković, M. (2026). Conceptual and Methodological Perspectives of Travel Time in an Integrated Passenger Transport System. Sustainability, 18(10), 5036. https://doi.org/10.3390/su18105036

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