Abstract
Keywords
Introduction
Because of the rapid development of the economy and the acceleration of urbanization, motor vehicle ownership and road traffic volume have dramatically increased. The demands from traffic on urban road infrastructure are becoming heavier because traffic congestion incidents more frequently occur.1,2 Traffic congestion at the intersection has seriously affected people’s daily travel activities and bring about environmental pollution and waste of resources. 3 On the contrary, convenient and smooth traffic at the intersection not only can greatly improve people’s work efficiency but also can improve the image of the city. It can be seen that research about traffic congestion at the intersection is necessary and significant. Traffic congestion at the intersection is complicated and changeable with many evaluation criterions. In other words, it is impossible to accurately assess the traffic congestion at the intersection depending on one criteria. Thus, multiple criteria decision-making (MCDM) method was introduced to study the problem of traffic congestion.4–6 Based on this, a scientific system was established to evaluate intersection congestion.
MCDM has been applied to a variety of traffic congestion evaluations. 7 Analytical hierarchy process (AHP) is a simple, flexible, and practical MCDM, which breaks down complex problems into several progressive levels and determines weight by comparing indices. 8 Techniques for order preference by similarity to an ideal solution (TOPSIS) is a classical method to MCDM problems; evaluation schemes are sorted according to the distance relationship among data sequences. However, combining TOPSIS and AHP offers more favorable results; in this combination, TOPSIS is used for design selection, and AHP is applied to calculate weights for the concerned criteria.9,10
However, AHP, TOPSIS, and gray relational analysis (GRA) all have their own respective defects. For example, although TOPSIS sorts evaluation schemes according to the distance to the ideal solution and negative ideal solution, the distance between evaluation schemes and the ideal or negative ideal solution may be equal. Furthermore, TOPSIS cannot reflect variation tendencies in the data sequence. Gray correlation (GC)11,12 takes the similarity of curves as a “yardstick” to reflect the change trends in the data sequence. GRA applies especially to poor information, but defects are evident in the overall assessment of evaluation schemes. In other words, the GC degree between evaluation alternatives and the ideal one may be equal. Therefore, neither TOPSIS nor GC is suitable for evaluating intersection congestion.
To more accurately and objectively evaluate traffic congestion, we proposed a new method that integrates fuzzy analytic hierarchy process (FAHP), TOPSIS, and GC to evaluate traffic congestion. Specifically, the FAHP is used to determine the preference weights of the evaluation index, and GRA subsequently is introduced to improve TOPSIS and combine Euclidean distance with the GC degree for the assessment of intersection traffic congestion. Overall, this hybrid method provides more reliable evaluation results. In this study, a novel method for assessing traffic congestion was determined by considering the weights of evaluation criteria, the location relationship among data sequences, and their situation changes. This article provides traffic management departments with constructive suggestions related to intersection congestion. Compared with previous studies, this article offers the following two noteworthy contributions:
A hybrid MCDM approach integrating FAHP, GC, and TOPSIS, called FGT, is proposed to evaluate intersection traffic congestion, making full use of quantitative analysis and the weight allocation features of FAHP and the selection abilities of GC and TOPSIS.
By comparing the proposed approach with the FAHP-TOPSIS and FAHP-GC methods, this research validates its effectiveness and feasibility in evaluating intersection traffic congestion.
The remainder of this article is organized as follows. Section “Literature review” describes the existing evaluation methods involving FAHP, TOPSIS, and GC. In section “Existing evaluation methods,” the novel evaluation method that combines FAHP, TOPSIS, and GRA is outlined. In section “The FGT method,” the method is applied to the evaluation of traffic congestion, and the effectiveness of this hybrid method is proven. Finally, the conclusions are presented in section “Assessment example.”
Literature review
MCDM provides a good ideal for multi-standard and complex traffic problems. Traffic system is a very complex task involving multiple criteria related to economic, environmental, and socio-political issues. MCDM techniques actually assist decision makers to choose the most reasonable program by assessing such problems. As far as we know, many methods exist for evaluating traffic problems: for example, the AHP,13–16 the FAHP,17–19 TOPSIS, 20 AHP-TOPSIS, 21 AHP-evidential reasoning,22,23 GRA, Decision-Making and Evaluation Laboratory (DEMATEL), and the AHP-TOPSIS-GC.24,25
At present, many scholars have done an in-depth study of traffic problems, and most of researches focus on MCDM techniques. For instance, Sadi-Nezhad and Damghani 26 adopt fuzzy TOPSIS method to assess the traffic police centers’ performance. Mohajeri and Amin 27 use AHP to select the railway station site. De Luca 28 uses AHP to handle the public engagement in strategic transportation planning. Awasthi et al. 29 adopt fuzzy TOPSIS to handle the Metro transportation problem. Arslan 30 uses a fuzzy AHP to evaluate transportation projects. Abbas 31 adopts MCDM techniques to assess such problems, most of which were related to transportation science. More detailed works refer to related reviews. 32 Moreover, MCDM approach has been applied to other traffic-related areas, such as airline industry, electrified vehicles, and logistic center, which is shown in Table 1.
Application of MCDM approach in traffic and related areas.
MCDM: multiple criteria decision-making; AHP: analytical hierarchy process; TOPSIS: techniques for order preference by similarity to an ideal solution; SMARTER: simple multi-attribute rating technique exploiting ranks; MCA: multi-criteria analysis; COPRAS: complex proportional assessment; SAW: simple additive weighting; VIKOR: vlsekriter-ijumska optimizacija i kompro resenje in serbian, meaning multi-criteria optimization and compromise solution; ELECTRE III: Elimination and choice translating reality III.
The review of the literature indicates that a large number of evaluation methods are applied to traffic system. But, very few people focus on the assessment of traffic congestion at the intersection. In order to fill the gap of the traffic system, in this article, the hybrid MCDM method integrating fuzzy AHP, TOPSIS, and GC is put forward for the assessment of traffic congestion at the intersection. FAHP is used to determine the weight vector of traffic index structure, which is established based on traffic system characteristics, that is, delay indicator, queuing indicator, saturation index, number of stops, and occupancy index. GC-TOPSIS is applied to obtain the final ranking of traffic congestion at the intersection.
Existing evaluation methods
The weight of each evaluation index in evaluating schemes is not the same. We introduced FAHP to determine the weights of indices more objectively and accurately in the TOPSIS and GC evaluation method.
The evaluation scheme was ordered using TOPSIS and GC, according to the Euclidean distance and the similarity between data sequences, respectively. Their basic evaluation steps are described as follows.
FAHP method
AHP was introduced by Saaty in the early 1970s; 52 however, its method for determining the weight is defective and complicated. Therefore, a MCDM method, FAHP18,19 was developed. At present, FAHP is applied to the evaluation of design schemes 53 and involves the following steps:
A certain element of the above grade is used as the evaluation criteria to compare two metrics at the corresponding level and determine the matrix element to construct a fuzzy judgment matrix
where
Fuzzy scale values and their meanings.
To ensure the accuracy and reliability of the final fuzzy matrix, the geometric mean technique was used to determine the final fuzzy matrix using formula (2)
where
To calculate the fuzzy weights of each indicator, the calculation process can be described as follows
Next, to obtain the fuzzy weight of each indicator, the following procedure is used
where
Standard weights denoted as
TOPSIS method
TOPSIS, proposed by Hwang and Yoon in 1981, is an effective method for solving MCDM problems. 54 A finite number of evaluation schemes can be sorted according to their distance to the ideal solution using TOPSIS, the results of which present the evaluative quality in the existing schemes. The ideal solution is the optimal solution that can be envisaged, wherein each attribute achieves the optimal value—in other words, the ideal solution maximizes the benefit or minimizes the cost. By contrast, the solution that maximizes the cost or minimizes the benefit is called the negative ideal solution. 55 The calculation steps of TOPSIS are as follows:
The structure of the initial decision matrix can be described using
where
The structure of the standardized matrix can then be described using
For the index where “the greater it is, the more desirable it is,”
For the index where “the smaller it is, the more desirable it is,”
Specifically
The ideal solution and the negative ideal solution are as follows
where
The calculation methods are as follows
The application of the formula is as follows
where
Thus, the TOPSIS analysis model evaluates the benefits and drawbacks of each solution on the basis of the Euclidean distance between each scheme and the ideal scheme. However, the Euclidean distance of two schemes may be identical; in this situation, we cannot determine the degree of superiority of these two schemes. Moreover, the distance to both the ideal and negative ideal solutions may be equal. This disadvantage of TOPSIS is outlined in Figure 1.

Case of equal Euclidean distance during TOPSIS analysis.
Points
GC method
GC analysis is a key part of the GC system, and it also is an effective method for the mining of data internal rule. GC analysis is based on analyzing the geometry of data sequences and the related degrees of curve geometry.56–58 Each scheme can be sorted according to the degree of similarity of the data sequence: the closer the curve shape, the bigger the GC. We can then interpret the principle of GC analysis intuitively.
First, the following four factors are assumed to be present in a data sequence
where

Comparison of data sequence curves.
Curve (0) is closest to curve (1); that is, they possess the most similar geometric shapes. We considered
The equation is
where
Next, the GC coefficient matrix between each scheme and the ideal solution is found
Finally, the GC degree
Next, the GC coefficient matrix is calculated using formula (20)
Finally, the GC degree
The FGT method
To compensate for the drawbacks of the TOPSIS method, and to more objectively and accurately evaluate the benefits and drawbacks of each scheme, this article proposes a novel evaluation method called the FGT method, which combines the FAHP, GC, and TOPSIS. The FGT method fully employs fuzzy theory to determine the weight of each evaluation index, as well as the GC and TOPSIS methods to sort the evaluation schemes. The following steps outline the FGT process:
where
where
where
The calculation process based on the description of the hybrid evaluation method is detailed in Figure 3.

Flowchart of the hybrid assessment method.
Assessment example
In this section, our hybrid evaluation method is applied to evaluate traffic congestion, and its effectiveness is reviewed.
Determining the evaluation index for degree of traffic congestion
To quantitatively consider the impact of traffic flow on the overall operation of the intersection and ensure that the evaluation results are scientific, comprehensive, and objective, the establishment of evaluation indicators should be scientific, objective, and comprehensive, as well as fully reflect the degree of traffic congestion. Depending on the situation at the intersection, this method uses five criteria as the evaluation index.
Delay indicator
Intersection delay is calculated by dividing the total additional travel time of the driver, passenger, or pedestrian by the effect of the control measures and of other road users by the flow through the corresponding cross section of the road. 59 It is a key performance index of intermittent traffic flow. This indicator determines the time loss caused by vehicles or pedestrians passing through intersections. The average delay is the most commonly used evaluation indicator of signalized intersections; overall, a greater delay value is indicative of a more crowded intersection.
Queuing indicator
Queue length is a useful index for evaluating the rationality of the design length of intersection entrances and the crowded conditions of intersections. Average queue length refers to the average length of the waiting queue of vehicles at each entranceway prior to the intersection60,61 and can directly reflect crowding at the intersection. Under normal circumstances, a longer average queue length is indicative of a greater amount of traffic.
Saturation index
Saturation is the ratio of actual traffic volume of a lane group at an intersection to its capacity. 62 Notably, total saturation refers to the saturation value reached by the phase with the highest degree of saturation, rather than the sum of phase saturation. Overall, a greater total saturation value is indicative of a greater amount of traffic.
Number of stops (parking rate)
Parking rate refers to the ratio of the delay time of deceleration–acceleration time. The average number of stops at the intersection (parking rate) can directly reflect the travel state of the vehicles at an intersection. Overall, a higher parking rate is indicative of a greater amount of traffic.
Occupancy index
Finally, time-share occupancy refers to the ratio of time that a car passes or stays in an entire observation period. 63 Time-share occupancy can be used to reflect the traffic flow of the corresponding imported lane.
Using these five indicators, evaluation indexes of traffic congestion can be clearly displayed (Figure 4).

Evaluation index of traffic congestion at intersections.
Determining the weights of five evaluation indexes of traffic congestion degree using the FAHP method
The five traffic congestion indicators were calculated using the FAHP method according to the following steps:
Calculated results of
BNP values of
BNP: best non-fuzzy performance.
Weights of each evaluation index.
BNP: best non-fuzzy performance.
Evaluation of traffic congestion degree
Value of traffic evaluation index.
Initial decision matrix.
Standardized matrix.
Standardized matrix
Ideal solution and negative ideal solution of the standardized matrix
Subsequently, the GC coefficient matrices
Comparison with existing methods
To verify the accuracy of the proposed hybrid evaluation method, the results of the FGT were then compared with the results of the FAHP-GC and FAHP-TOPSIS methods. The weights that were determined using FAHP were subsequently applied to the three evaluation methods. The evaluation result of FAHP-GC was obtained using formulas (24) and (25), where
Closeness index of the three methods.
FAHP-GC: fuzzy analytic hierarchy process–gray correlation; FAHP-TOPSIS: fuzzy analytic hierarchy process–techniques for order preference by similarity to an ideal solution; FGT: FAHP, GC, and TOPSIS.
Table 11 indicates that the evaluation results of the three methods are consistent for the degree of traffic congestion. The validity and accuracy of our proposed method are confirmed through data comparison. Moreover, the data clearly indicate that the FAHP-TOPSIS evaluation method cannot effectively compare the two time periods of traffic congestion when there are two sets of equal data. However, the proposed method is a comprehensive evaluation method that is based on Euclidean distance and data sequence curve similarities. This evaluation method overcomes the shortcomings of FAHP-TOPSIS and FAHP-GC, rendering the evaluation results more accurate and reliable. In summary, the proposed method is feasible and effective for evaluating traffic congestion at intersections.
Conclusion
Traffic decision-making plays a significant role in urban public transport planning; in this article, traffic congestion can be effectively evaluated by a hybrid MCDM method combining the FAHP, TOPSIS, and GC techniques. Obviously, the MCDM method combining FAHP and TOPSIS has proved to be defective when evaluating the traffic congestion degree because FAHP-TOPSIS cannot accurately evaluate two schemes in Table 10 that have equal distance from the ideal solution. Similarly, FAHP-GC mainly focuses on situation changes among data sequences. It may not be precise enough and thus leads to some misleading conclusions without considering their comprehensive features.
In this work, the ranking results are compared with commonly used MCDM methods involving TOPSIS, GC, and FAHP. The results demonstrates that the proposed method can be used to solve real-life MCDM problems in urban public transport planning, and the method can provide an accurate evaluation of the alternatives and offer a more reasonable selection. The main novel elements of the proposed method are summarized below. First, the proposed method overcomes the shortcomings of the FAHP-TOPSIS and FAHP-GC methods, and it can be used as an accurate and effective multi-attribute scheme decision-making method. Especially, FAHP is determined as the technique of weight assignment, thus reducing the influence of subjective preference. Second, FGT is a useful and reliable tool for evaluation of traffic congestion degree based on the results of an empirical case, comparison analysis. A suitable hierarchical structure of each criterion considering delay indicator, queuing indicator, saturation index, parking rate, and occupancy index is built for intersection traffic congestion evaluation, and the reasonable weight for each criterion is derived. Third, this method can be used to guide decision makers in making better decisions when constructing a best intersection and traffic congestion control. Moreover, the proposed approach can be applied to other fields, for example, selection of suppliers and plant location selection.
With the advancement of science and technology, and the development of multi-attribute theories, we predict that new theories and methods can be identified and integrated to assess traffic congestion. In particular, we suggest that uncertainty theory should be considered in multi-attribute decision-making. 64
