Decision support system for evaluating park & ride system using the analytic hierarchy process (AHP) method

ABSTRACT The park and ride (P&R) system is a crucial transfer point between private and public transportation, playing a significant role in the sustainable urban mobility plan (SUMP) and operational objectives of the system. The implementation of the P&R system requires careful consideration of diverse criteria related to private vehicles and public transport, which must be evaluated by transportation planners with expertise in transportation, road safety, and mobility. When determining the optimal location for the P&R system, transportation planners specializing in transportation, road safety, and mobility must take a number of criteria into account. This paper discusses the use of the analytic hierarchy process (AHP) for establishing a P&R system. In addition, the multi-criteria method permits consensus on the primary criteria for the location of the P&R system in an intermediate city. The result shows that accessibility to public transportation has been identified as the most important criterion for establishing a P&R system by transportation planners. In conclusion, the AHP is a multi-criteria method that allows transport planners to evaluate the location of the P&R system.


Introduction
Numerous factors must be taken into account when determining the location of the P&R system, as transportation experts have extensive knowledge of numerous mobility sectors (transportation, transit, environment, and policy).The purpose of using the P&R system is to drive from the residential district, park the vehicle, and then take public transit to the destination central business district (CBD); therefore, proximity to a public transit station is one of the most important criteria for the location of a P&R system.According to Li et al. (2007), the connection to a transportation system is essential to the success of the project, because the P&R system serves as an interchange point for public and private vehicles.This is supported by Liu and Meng (2014), who proposes that when locating a P&R system, it should be a priority that it serves as a modal interchange point and helps transform the paradigm of private transport users, allowing them to gradually abandon this mode of transportation.This is not, however, the only requirement for locating a P&R system.Therefore, the problem of the criteria and sub-criteria for the location of a P&R system arises.Each of them must be evaluated to determine which criterion is the more important one.
In addition, the parameters and the location of a P&R system are determined by the type of the city; therefore, an examination of mobility plans provides insight into the criteria and location of a P&R system.To avoid making unnecessary investments in the location of the P&R system, municipal decision-makers, transportation project financing experts, mobility experts, and public transport experts must utilize their expertise.
The P&R system is designed to achieve certain mobility goals, such as reducing traffic pollution in the city centre, decreasing the number of vehicles on the road, and promoting the use of public transportation.All of these goals raise questions regarding the justification for installing a P&R system.This creates a problem of uncertainty in determining which criteria experts consider, so a decision maker (DM) will typically select or rank alternatives based on intangible or incompatible characteristics using multi-criteria decision-making (MCDM).To achieve the mobility objective of the P&R system, transportation personnel and planners must concur on the criteria to be prioritized in establishing the P&R system.Determining which parameter is the most crucial requires a complex decision-making process driven by multiple competing goals.
The evaluation of a P&R system involves the consideration of multiple criteria, such as accessibility, cost, safety, and environmental impact.Determining which parameter is the most crucial requires a complex decision-making process driven by multiple competing goals.The AHP method is a widely used decision support system that allows decisionmakers to prioritize and compare different criteria based on their relative importance.However, the application of the AHP method for evaluating P&R systems requires careful consideration of the underlying assumptions and limitations of the method.Additionally, the decision-making process must be transparent and involve the input of all relevant stakeholders to ensure that the final decision is acceptable and sustainable.Solving this research problem as the article's goal will help readers understand the significance of evaluating the P&R system and its contribution to the field of transportation planning.
Although multi-criteria methods have been utilized in a number of transportation studies to locate modal interchange points, they have not been systematically implemented in the P&R system.Therefore, this article will contain contributions from various disciplines.First, from the perspective of transport planning, specifically in Latin American cities where this research is being conducted to determine the most important criteria to consider when establishing a P&R system.Second, establish a set of criteria from a novel scientific perspective.Lastly, from a methodological standpoint, locate the P&R system using a multi-criteria technique such as AHP.
The rest of the article is structured as follows.Section 2 describes the main highlights of AHP and applied studies in the field of transportation and P&R.Section 3 describes the selection of criteria, the AHP methodology, and the hierarchical structure.Section 4 presents the findings and discussion together.Finally, the concluding section reviews the essential findings and sets future directions.

Literature review
Multi-criteria decision analysis supports transportation project decisions by involving stakeholders i.e. transportation experts with different specialties (de Brucker et al., 2013;Macharis et al., 2009).The decision-maker can specify the primary and secondary criteria for making a decision in advance, using the multi-criteria approach.A multi-criteria method is appropriate because the local government's objective on the P&R system is focused on what is stipulated in the SUMP, as well as the operation of the P&R system.Consequently, each group of experts in various specialties can choose the criteria according to their expertise.Therefore, a multi-criteria procedure includes methodological process of criterion selection and application to synthesize the views using a computational approach (Janiak & Żak, 2014;Moslem & Çelikbilek, 2020).Given the number of variables to consider and the importance of making a decision that can be implemented, it makes sense to investigate multi-criteria (MCDM) methods for public transportation planning (Moslem et al., 2023;Suganthi, 2018).Methods that are based on MCDM are often used in transportation projects (Mardani et al., 2015) and, the AHP approach is rapidly becoming one of the most preferred MCDM methods that offer support to decision-makers (Saaty & Vargas, 2013).AHP is an appropriate tool for decision makers who are faced with issues that require them to consider multiple criteria and multiple stakeholders because it can handle problems that are typical of complex scenarios.In comparison to other MCDM techniques (such as PROMETHEE, ELECTRE, and TOPSIS) (Chatterjee & Kar, 2016;Sun, 2010), the AHP provides evaluators with a clear hierarchical decision structure.This is useful in situations where individuals with different levels of expertise are involved, such as when designing and building a P&R system (Pedroso et al., 2018).The AHP method is not a statistical technique; rather, it is a dynamic analysis that reflects the actual perception of the problems by stakeholders through a dynamic questionnaire (Fu et al., 2018).The various applications of this method have been successfully carried out in the field of transportation.For example, AHP can be used to identify public transport performance problems in various cities, so that solutions can be developed and applied to solve the optimization problem.The public transport criteria have compared the performance of different operators working under similar conditions and identify the public transport operator with the best overall performance (Duleba, 2019).In order to provide better outcomes to decision-makers, an AHP approach to evaluating the performance of urban public transportation organizations is divided into categories such as 'operational', 'financial', and 'accident-based' (Suganthi, 2018).
The P&R system has been established over time as part of the transport infrastructure of cities, especially European cities, but in developed Latin American cities, this type of system is still little known.As its concept works as a modal interchange, it is ideal from the transport planner's point of view that private transport users opt for a less polluting option such as public transport to reach their destination.
Literature on planning a P&R system includes methodologies and mathematical techniques for establishing strategic locations at which to implement P&R facilities (Aros-Vera et al., 2013).For example, a parking choice model has been developed that consisted of a survey of household travel to public transport, which was used to estimate a model of parking station choice (Habib et al., 2013).In turn, the location of the P&R system has been studied based on Euclidean distance to know which parking lot is the closest from the residential area.Continuing with the research carried out on the P&R system, there are choice models known as multinomial that attach parameters of potential users such as age and travel motive.In this sense, it is possible to know the criteria that researchers have taken into consideration to establish a P&R system, which evidently are distance and travel times (Fan et al., 1993;Pang & Khani, 2018) (Ebrahimi and Bridgelall, 2021).
A criterion that can be broadly summarized is related to aspects of public transport such as frequency of transport service, travel time, and accessibility.Sharma et al. (2019) conducted a more detailed study on the choice of access to public transport using household travel survey data.In addition, studies on public transport choice models using the P&R system found that the mode of access to a transport stop is related to the choice of the parking facility, and also included in their research travel attributes, vehicle availability and the price of parking (X.Chen et al., 2018).
A criterion that has been studied in traffic and is related to the operation of the P&R system, is that the P&R system is a policy that helps to reduce trips to the city center in private vehicles, and therefore diminishes traffic that was destined for the CBD (Sharma et al., 2019).
Although AHP is used to solve a variety of problems involving multiple criteria, such as improving public transportation quality, it has not been used in the P&R system to determine which criteria are appropriate for the facility's location.The AHP method does not work well for all types of research and may have some flaws, such as producing unreliable results.Nonetheless, it remains the most widely used research method (Feizizadeh & Ghorbanzadeh, 2017).A common limitation of AHP is that there may be multiple groups involved in a problem, and it is difficult to express their opinions in the pairwise comparison matrices using numbers (de Brito et al., 2018).
Sometimes those responsible for making decisions do not fully comprehend the nature of the criteria, or they have their own preferences regarding the comparison of criteria (Lehner et al., 2018).In addition, not all groups or members of a group will agree on the importance of a given criterion, and they will almost never agree on an exhaustive list of weights for decision-making purposes (Ortega, Moslem, et al., 2021).When attempting to solve a fully participatory multicriteria problem, the inherent difficulties of the AHP become even more apparent.
It is unclear whether AHP can adequately deal with a participatory situation in which the decision-makers involve a number of transportation experts with different types of expertise (Cabrera-Barona & Ghorbanzadeh, 2018).Even a seemingly insignificant change to the way the criteria are weighted can have a substantial effect on their presentation order.A large number of studies have attempted, with varying degrees of success, to reduce the inherent uncertainty in the AHP method in the light of these issues.Some research has suggested the implementation of sensitivity and uncertainty analysis, as well as the integration of AHP with statistical methods such as the Monte Carlo simulation (Ghorbanzadeh et al., 2018).Under specific conditions, the Fuzzy AHP method, which is based on a variety of membership functions, is regarded as an efficient and adaptable technique (Larimian et al., 2013).In addition, interval calculation has been incorporated into AHP pairwise comparison matrices to improve the dependability of the weighting results, as well as to expand the range of questionnaires that can be used to generate a given set of results and make them more flexible (Entani & Sugihara, 2012).This integration aids in the resolution of problems requiring a variety of experts and questionnaire formats.When it comes to the same questions, various experts frequently reach wildly divergent conclusions, which can create complications.Calculating in intervals is also more practical when experts are uncertain about the values they are employing and instead choose to use AHP to make a difficult decision (J.Chen & Yang, 2011).
The studies presented in the literature (Lakusic, 2018) about the P&R location problem have used mathematical methods, algorithms, surveys, mode choice, but not the multi-criteria method known as AHP.The P&R system has even come to be seen as a transportation policy in SUMPs to decrease the traffic caused in the CBD.The literature shows the criteria that experts have found suitable to solve the location problem individually.This research contributes to collect all the criteria that have been selected individually and classify them in order to apply the AHP multicriteria method and to determine which criteria are the most relevant for the location of a P&R system.

Development of a decision-making model to evaluate P&R systems
Before understanding the model, it is useful to explain the P&R approach in order to comprehend the evaluating criteria.The conceptual model of a P&R system is a trip that begins with a private vehicle, and parks, and then continues with public transportation to its final destination; in other words, the trip involves an interchange of modes of transportation.Consequently, the criteria will be related to private transport, public transport, P&R operation, and parking policy requirements outlined in the city's Sustainable Mobility Plan (SUMP) (see Figure 1).

Criteria description and selection
To answer the question of what criteria should be considered when implementing a P&R system, we began by reviewing the published works of experts who have offered a variety of perspectives on the topic of implementing a P&R system.The second point is the city's parking mobility plan's concept, and the third and final point is the P&R system's operational purpose.According to specialized literature (Z.Chen et al., 2014), one of the criteria to be considered is proximity to public transportation or public transportation stations, as well as the total duration of the trip.It has also been demonstrated that the P&R system reduces pollution by restricting trips to the city center and decreasing the number of private vehicles in the central business district (CBD).
On the other hand, the SUMP has allowed the municipality to determine what type of city it desires in the future and what parking recommendations transportation planning experts have based on the mobility plan.The mobility plan for Cuenca (Ecuador) includes park-and-ride lots to help decongest the central business district (CBD) and reduce the use of private vehicles, while integrating it into a new mobility model (see Figure 2).
The conceptual model of the P&R system as a modal interchange between private vehicles and public transport provides the basis for the P&R's operational system, which can be described as follows (See Figure 1).
After ranking the criteria, a total of 25 criteria were selected from the aforementioned three concepts, and the levels for applying the AHP model were established.Following the six criteria comprising the first level, denoted by the numbers C1 through C6, there are a total of 19 sub-criteria, denoted by the numbers C1.1 through C6.3.The first digit of each sub-criteria number indicates the corresponding primary criterion.Then, ten transportation experts employed by the municipality of Cuenca were polled to determine the most important criteria.Figure 2 depicts the criteria and sub-criteria to clarify their distribution and relationship to the SUMP and the operational portion of the P&R system.

Analytic hierarchy process (AHP)
This MCDM method facilitates the resolution of a challenging problem involving a P&R system.In 1980, Saaty developed the analytic hierarchy process (AHP), which is now used to model and rank factors in many different industries and disciplines, including management, manufacturing, industry, government, and engineering (see Table 1).The method is known as MCDM, which is used extensively in transportation projects all over the world.
Evaluators should perform pairwise comparisons for all elements of the model, taking into account hierarchy levels.For the first level, the following criteria were formulated: C1, C2, C3, C4, C5, C6.For the second level C1.1 to C6.3During the AHP process, the consistency of answers was examined by Saaty's Consistency Index (CI) and Consistency Ratio (CR) < 0.1, because the experiential matrices most of the time are not resistant: where CI is the consistency index, λ max is the maximum eigenvalue and n is the number of rows in the matrix.CR can be determined by: where RI is the random consistency index If A is a consistency matrix, A � X ¼ λ max X.
Then eigenvector X can be calculated as A À λ max I ð ÞX ¼ 0, where λ max is the maximum eigenvalue of the matrix A. λ max is the principal eigenvalue of the matrix A. For determining the eigenvectors of the aggregate matrices, the following method was applied: where j ¼ 1; � � � ; m and w j >0 (j ¼ 1; � � � ; m) represents the related weight coordinate from the previous level; w ij > 0 (i ¼ 1; � � � ; n) is the eigenvector computed from the matrix in the current level, w A i (i ¼ 1; � � � ; n) is the calculated weight score of current level's elements.The consistency ratio (CR) was acceptable to complete the AHP analysis

Results and discussion
The experts selected the highest ranking criteria for levels C1 through C6.The results of the AHP model revealed that, with a score of 0.355, C3 has the highest criterion value and is positioned first in the ranking.While C2 is the lowest criterion in the ranking with a value of 0.065 (see Table 2).
The main criterion for establishing a P&R system in a Latin American city such as Cuenca, Ecuador, is public transportation accessibility (C1) (Figure 3).This supports what some authors (Carlson & Owen, 2019;Cherrington et al., 2017) arrived at and the P&R concept, which is that the P&R system should be established with connections to Table 1.Judgment scale of relative importance for pairwise comparison (Saaty, 1977(Saaty, , 1980)).public transportation.The environmental conditions C6 are the second criterion in the ranking.This also supports what some authors (Hou et al., 2020;Molan & Simicevice, 2018;Ortega, Tóth, et al., 2021) claimed about the route's reduced traffic and, as a result, pollution.C4, which refers to general aspects of transportation, is the next highestranking criterion.However, one of the least important factors in implementing a P&R system is the economic aspect.This refers to criterion C5, because the objective of P&R is not to economize costs.Another non-essential criterion is C1, which is distance, i.e. since most of the citizens who could use P&R systems have private vehicles and live outside the city, they will be able to travel any distance.The C2 is the traffic on the entire route, and it is ranked last and least important.As a result of the P&R system, the first track of the journey is completed by a private vehicle, and the second track is completed by a public bus, which will have roadway priority.
The 19 proposed sub-criteria vary on this scale, which is the most difficult to interpret.As a result, the analysis was divided into two sections: first, the local classification is discussed, then the global classification is addressed (see Table 3).
The local ranking compares the sub-criteria with the main criterion.In other words, criterion C1 refers to distance.C1.1, the distance from the origin to the P&R system, is the main sub criterion, followed by C1.2, which refers to the distance from the P&R system to the CBD.That is, in distance aspects of establishing a P&R system, the distance from the area of residence to the P&R system is more important.Transportation planners should consider this aspect as a priority when referring to distance (see Table 3).In criterion C2, which refers to the traffic conditions of the complete route when taking the P&R system, the main sub-criterion is C2.3, which refers to the completion of the trip from the origin, which is the residential area, to the destination, which is the CBD.The second most important sub-criterion is C2.2, which refers to the public transport time from the P&R system to the CBD destination.In the last position we find the sub-criterion C2.1.which refers to the time from the origin to the P&R system.Most importantly, transportation planners should take into consideration the total time from origin to destination using the P&R system (see Table 3).
The accessibility of public transport is addressed by criterion C3.C3.1, which refers to the frequency of public transportation to the P&R system, is the most important subcriterion.The next sub-criteria is C3.3, which addresses the distance between the P&R system and the public transportation station.Transfer time is the subject of sub-criteria C3.2, which occupies the final position.In other words, transport planners and experts in establishing a P&R system in a city should take into consideration the optimization of public transport and especially focus on the frequency that public transport provides service to the P&R system (see Table 3).
The primary criterion C4 is concerned with the overall aspects of transportation.The main sub-criterion is C4.2, which refers to the rising demand for public transportation.It is followed by C4.1, which addresses the reduction of private transportation trips to the central business district.The next sub-criterion is C4.3, which refers to the current public transportation supply.Lastly, there is C4.4,which is the P&R system's demand.In this main criterion, one of the most important considerations when implementing a P&R system is increasing demand for public transportation while reducing the number of vehicles in the CBD, which necessitates the presence of vehicle parking spaces in the P&R system (see Table 3).
The main criterion C5 refers to the economics of establishing a P&R system.The main sub-criterion is C5.2, which refers to the P&R system's land use cost.This is followed by sub-criterion C5.1, which refers to the total costs of putting the P&R system in place.C5.3 is the next sub-criterion, and it refers to the total cost of the technological system when implementing the P&R system.Finally, sub criterion C5.4 is the investment cost, which determines whether the project will be handled publicly or privately.The cost of land use in establishing the P&R system is the most important thing to know in the overall analysis of the economic criteria, because transportation planners know that the P&R system is established in places where land use is costly and, in general, the limited space in cities makes acquiring these spaces difficult (see Table 3).
The main criterion C6 refers to the environmental aspects of putting in place a P&R system.C6.1, which refers to CO 2 reduction, is the primary sub-criterion.Sub-criterion C6.2 refers to noise reduction as a result of fewer vehicles entering the CBD.Finally, subcriterion C6.3 discusses existing green areas, specifically how the P&R system can contribute to the availability of space to implement green areas.The planners consider the reduction of pollution and noise as an important aspect of using the P&R system to reduce private cars in the CBD in an overall analysis of the main environmental criteria for establishing a P&R system (see Table 3).
The following is an overview of the AHP analysis of the sub-criteria.The most important sub-criterion, C3.1, refers to the frequency of public transportation to the P&R system.This is followed by criterion C6.1, which addresses the reduction of CO 2 emissions through the implementation of the P&R system.Sub-criterion C3.3 refers to the distance between the P&R system and the public transportation station.Continuing with sub-criterion C4.2, increasing demand for public transportation to the CBD.In this sense, a general analysis and discussion of the main sub-criteria confirms what has been analysed in the literature and corroborated in this study, where the main sub-criteria refer to the connection between public transportation and the reduction of aspects such as pollution.In other words, transportation planners believe that connection and accessibility to public transportation are the most important factors in determining the location of a P&R system (see Figure 4).
Sub-criterion C1.1, which is ranked fifth and has to do with residents' proximity to the P&R system, is followed by sub-criterion C6.2, which has to do with noise abatement.C4.1 is at position 7 in the ranking and refers to the reduction of private vehicle trips to the CBD.Then comes sub-criterion C3.2, which is the time it takes to get from P&R to public transportation.C5.2 is the cost of implementing a P&R system in terms of land use.The number of public transport connections is followed by sub-criterion C4.3.Furthermore, C6.3 represents the number of occupied green areas that can be extended to the P&R system.According to an overall analysis, these sub-criteria are important on a medium scale of the P&R system.In other words, planners believe that these elements should be considered but are not a top priority when developing a P&R system (see Figure 4).
The following sub-criteria can be listed in decreasing order of importance.C3.2 refers to the time it takes to get from the P&R to public transportation.C2.2 is the public transportation time when using the P&R system.C5.1 represents the project implementation cost.In addition to C5.3, which is the cost of implementing infrastructure.C5.4 is the investment cost sub-criterion.Sub-criterion C4.4, which is the demand for the number of P&R system spaces.Sub-criterion C1.2 refers to the distance from the residential area to the P&R system, and sub-criterion C2.1 refers to the time taken by a private vehicle.In other words, experts believe that the time spent in private transportation when using the P&R system is the least important sub-criterion to consider when establishing a P&R system.Planners understand that to shift the paradigm from private vehicle users to public transportation, the P&R system must be designed with public transportation optimization in mind.Furthermore, the experts' responses validate the basic concept of P&R being a modal interchange in this study (see Figure 4).
A combinatorial analysis of the main criteria and sub-criteria reveals that the main criterion that transportation planning experts consider when implementing a P&R system is public transportation accessibility.This is consistent with what has been studied in the literature throughout the document, which has primarily established that the P&R system serves as a modal interchange point between private vehicles and public transportation.That is, transportation experts from various specializations have agreed that optimizing public transportation is critical when it comes to locating the P&R system in the urban environment.Furthermore, the sub-criteria support this, with the main subcriterion being the frequency of public transportation to the P&R system.
When establishing a P&R system, planners should consider the frequency of transportation; that is, a P&R system should not be established if the optimization of public transportation in various aspects is not guaranteed.An important aspect of the subcriteria was that the use of a P&R system reduces the number of vehicles in the city centre, resulting in lower pollution and noise levels.
Concerning the analysis about the studied literature, this study proves what some researchers have already realized that the P&R system is created as a modal interchange point in which public transport and its operation is fundamental.The second point of analysis is that, according to the SUMP, P&R systems are designed to reduce traffic and pollution.Additionally, this study has determined that P&R systems are designed by experts with these objectives in mind, proving that the SUMP and parking section policies are effective.Finally, according to the operation of the P&R system which is from an origin to travel a certain distance to the P&R and then use public transport to reach the CBD destination.This study proves that the operation in the second part of the trip should be optimized specifically the one using public transport.This study confirmed the objectives of finding out, in three specific aspects based on the literature on SUMP and parking policies, in addition to the operation of P&R, what the main criteria according to transport experts with different expertise are when establishing a P&R system in the urban area of the city using a multi-criteria method of AHP.One limitation is that this study was applied to a Latin American city with unique mobility needs.However, it would be beneficial if this study could be applied in the near future to cities with other SUMP objectives in order to see the point of view of experts in that context.

Conclusion
The study consisted of applying a multi-criteria method known as AHP to determine which criteria and sub-criteria are the most important for transportation experts in different specialties to establish a P&R system in a Latin American city.The study had 6 main criteria and 19 sub-criteria.The criteria and sub-criteria were extracted based on three axes where information on the P&R system exists.The first is on the existing literature on P&R, the second is on transportation planning and specifically on the SUMP, and lastly on the operation and functioning of the P&R system.
The result shows which criteria are fundamental when establishing a P&R system.Thus, according to the six main criteria established, the most important is the criterion on accessibility to public transportation.This criterion is fundamental within the three analysed aspects.In other words, optimizing public transport is fundamental when establishing a P&R system.The least relevant criterion considered by the experts is the traffic conditions along the entire route of the P&R system, i.e. this aspect is based on the operation and functioning of the P&R system.As for the sub-criteria, the most relevant one according to the experts for establishing the P&R system is the frequency of public transport to the P&R system, which is directly related to the main criterion of accessibility to public transport.On the other hand, the least relevant sub-criterion is the distance travelled by the private vehicle from the residential area to the P&R system.This leads us to consider that the P&R system functions as a transport policy that allows modal interchange and that its accessibility and optimal functioning with public transport must be guaranteed.
The AHP method considers several criteria to evaluate the decision-making process.The main criterion for establishing a P&R system in a Latin American city such as Cuenca, Ecuador, is public transportation accessibility (C1).This finding aligns with the P&R concept, which suggests that the system should be established with connections to public transportation.The accessibility of public transportation can improve the convenience and affordability of the P&R system, making it an attractive option for commuters In future studies, this method and criteria developed could be applied to different types of cities in different parts of the world.This could help to understand the placement of the P&R system and its application criteria in the urban environment of a city.Modifying the criteria according to the reality of the city is also appropriate.Also, adding new criteria such as new transportation technologies including electric or autonomous vehicles is also a relevant option.

Figure 2 .
Figure 2. Model for the determination of criteria for establishing a P&R system.

Figure 3 .
Figure 3. Results of applying the AHP model at the primary level.

Figure 4 .
Figure 4. Results of applying the AHP model at the second level.

Table 2 .
Ranking of main criteria.