Evaluation of Road Traffic Vulnerability in Urban Agglomerations Based on Entropy Weight-TOPSIS Model

Aiming at the problem of increasing road traffic vulnerability in urban agglomerations year by year, this paper proposes a practice-oriented model and method. Firstly, the index system of urban agglomeration road traffic is established on the basis of analyzing and sorting out relevant planning and design indexes at home and abroad. Secondly, based on principle, an evaluation model of urban agglomeration road traffic vulnerability based on entropy weightmodel was constructed. Finally, an empirical study was conducted to calculate the indexes with software, and the corresponding indexes were put into the model for calculation. By comparing the calculated results with the grade classification standard, the vulnerability of the urban agglomeration and the corresponding urban road traffic was judged and the corresponding improvement Suggestions were put forward.


Foreword
So far, urban agglomeration road traffic vulnerability has studied by some of the domestic and foreign scholars. Junmei Wang has evaluated the road traffic emergency response capability at the perspective of vulnerability when it faced with sudden events [1]. European scholar named Jenelius and other authors determined the vulnerability of road sections in terms of emergency capacity assessment by constantly removing single road section until certain paths or road networks became unconnected [2]. There have been many researches on the application of methods in the field of transportation. Xinxin Yan and other authors evaluated the coordination between slow traffic and urban design [3]. Chai Li and other authors studied the optimization of alternative schemes for environmental impact of traffic planning based on method [4]. Wenbin Luo and other authors evaluated and studied the coordination between Hangzhou's urban tourism and urban development by using method [5]. Ying Wang and other authors evaluated four optional schemes of Xi'an rail transit network by combining model, AHP method and entropy weight method, and then the optimal solution is selected [6].
In a word, most domestic and foreign scholars have applied method to the research on the vulnerability of a single city, but have not systematically studied the urban agglomeration. However, with the increasing significance of city clustering, taking urban agglomeration as the research object has become a trend in the field of transportation. Based on it, on the basis of building an evaluation index system of road traffic vulnerability in urban agglomeration, this study established an evaluation model of road traffic vulnerability in urban agglomeration by using the entropy weight-model to evaluate the vulnerability of road traffic in urban agglomeration.

Construction of index evaluation system of road traffic vulnerability in urban agglomeration
According to the quantifiable principle to compare and select evaluation indexes, and draw lessons from the domestic and foreign related evaluation index system, this study on the influencing factors of urban road traffic vulnerability analysis as the breakthrough point, finally construct an index evaluation system of urban road traffic vulnerability as shown in table 1, the calculation method  of the indexes in table 2 and table 3. In the index evaluation system, the higher the value is, the better the index is called positive index, and the smaller the value is, the better the index is called negative index. As for the factors affecting the vulnerability of road traffic system in urban agglomerations, this study explored the following indexes, as shown in table 1.    Table 3. Positive indexes and its calculation methods

The name of the indexes Calculation formula Meaning
Average path length

The establishment of the process of entropy-TOPSIS model
Step one: The original matrix of the entropy-TOPSIS model is shown as follow：the urban agglomeration has m cities called 1 2 , ,..., m S S S ， every city has indexes 1 2 , ,..., n C C C 。 ij a represents the number of the Step two: The index matrix of the original urban agglomeration is processed and the normalization matrix is obtained through calculation. Step (2)Standardized processing：The above judgment matrix is standardized to obtain the standardized judgment matrix *12 For positive indexes，the calculation formula is shown in (1) : For negative indexes，the calculation formula is shown in (2) : Step five: Calculate the distance between the most vulnerable and the least vulnerable cities in each urban agglomeration, the calculation formula is shown in (5): In this study, the vulnerability status of road traffic emergency carriers is divided into five levels, as shown in

Acquisition of data of vulnerability assessment index system of road traffic in urban agglomeration
In this study, the urban agglomeration of Hohhot, Baotou, Ordos and Yulin was selected as the research object for case study. Figure 1 shows the road connection profile of the urban agglomeration of Hohhot, Baotou, Ordos and Yulin by using software. Each station is taken as a node, and the figure is used to calculate the 12 indexes by combining data and formula.

Figure 1 Road condition connection map of urban agglomeration
Pajek software was used to calculate these data by substituting the relevant formula in 1, and 9 relevant indexes including positive index and negative index were calculated respectively. The results are shown in table 5  and table 6.

The calculation process and analysis
Step one: The original matrix of the entropy-TOPSIS model is obtained from 2.1 as follows: Step two: Deal with the index matrix of the original urban agglomeration and obtain the normalized matrix through calculation as follows: Step three:The weight of road traffic vulnerability assessment indexes in each urban agglomeration is considered.The original judgment matrix is: The original judgment matrix is: The normalized matrix is: The weight values of positive and negative indexes in the final evaluation indexes are calculated as shown in table 7 and table 8: Step four: Determine the various indexes of the Step five: Calculate the distance between the most vulnerable and the least vulnerable cities in each urban agglomeration The most vulnerable is： The least vulnerable is:  in table 7 and table 8 were substituted into the  TOPSIS model, and the positive and negative ideal  values and relative closeness degree of the city group  were obtained through calculation, as shown in table 9  and table 10. The final calculation result is: According to the calculation results, for the overall urban agglomeration, the vulnerability level of the traffic management system in this research area is high, with an average degree of closeness of 0.67. In the face of unexpected events, the loss is relatively high. The government should strengthen the management of the local level, to ensure that the local traffic safety, orderly, and efficient manner. To avoid the happening of the emergency, they can mobilize the broad masses of security companies to actively participate in the security of urban traffic construction. At the same time, improving the transport infrastructure, expanding the scale of construction and improving the traffic concept. For each city in the urban agglomeration, it is necessary to improve the road conditions in combination with the local actual conditions to bring more convenience to road traffic users.

Conclusion
In this study, an evaluation model of road traffic vulnerability of urban agglomeration based on entropy weight-TOPSISmodel was established. Pajek software was used to study the urban agglomeration of Hohhot, Baotou, Ordos and Yulin. The case study proved that the established index system and model were reasonable and feasible. The research results are as follows: (1) The final judgment of the vulnerability of an urban agglomeration is the average vulnerability, so the vulnerability of the urban agglomeration is closely related to the vulnerability of each city in the urban agglomeration. If the vulnerability of the entire urban agglomeration is to be reduced, the vulnerability of each city can be reduced as the entry point.
(2) The vulnerability of urban agglomeration is closely related to the local conditions of each city. According to the evaluation index system of urban agglomeration road traffic vulnerability, the local government can analyze and improve the local road conditions from the two directions of reducing negative indexes and improving positive indexes.
(3) The construction of the evaluation model makes the formulation of the traffic planning scheme have a more profound guiding significance. In the practical application process, more comprehensive evaluation indexes should be used according to the specific situation, so that the formulation process of the traffic planning scheme can be truly scientific and strict.