| The number and length of freeway tunnels is increasing every year because of their irrepl aceable advantages in terms of improving alignment and reducing travel times.However,as a special semi-enclosed,tubular structure,highway tunnels are accident-prone due to a series of characteristics such as restricted internal space and a huge difference in illumination between the inside and outside of the tunnel.The alignment parameters and the speed in the freeway tu nnel affect the safety of traffic in the tunnel.The alignment of the road changes rapidly with ti me and location,while the speed of traffic changes as the alignment changes.In order to ensur e the safe operation and efficiency of freeway tunnels,it is necessary to study the safe operati ng speeds in tunnels based on alignment parameters and traffic characteristics.This paper pro poses a method for determining safe operating speeds based on alignment parameters.This m ethod takes into account the actual road conditions and is of great importance in improving th e efficiency and safety of traffic in freeway tunnels.This paper first analyses the relationship between alignment,vehicle speed and traffic saf ety to verify the feasibility of this research.This is followed by a review of relevant research o n the methods and basis for determining safe speed values for freeways at home and abroad.T hen,the four aspects of driver,vehicle,road and environment are qualitatively analysed in ter ms of their mechanisms affecting the safe operating speed of freeway tunnels.On this basis,t he safe operating speeds of large trucks and cars on straight and curved sections are quantitati vely analysed and calculated from the perspective of ensuring sufficient stopping sight distanc e for drivers in freeway tunnels,based on the alignment parameters.It is proposed to divide th e speed zones according to the different alignment elements,and to set a buffer zone for accel eration and deceleration at the interface of each adjacent zone,and to calculate the length of th e buffer zone based on the acceleration and deceleration process of drivers.Then,the three evaluation indicators of speed standard deviation,traffic conflict rate and traffic efficiency are proposed to evaluate the speed scheme on the premise of safety and effici ency,and the three indicators are calculated by using the data such as vehicle speed in the mer file output from VISSIM simulation.As the sensitivity of speed changes to changes in the thr ee indicators is different,the CRITIC method is used to calculate the weights of the three indi cators and then find the safe operating speed of the highway tunnel under their common const raints through the weighted average method.The speed values obtained were compared with t hose derived from the previous stopping sight distance model,and the smaller of the two was selected as the speed limit value in the freeway tunnel.Finally,the traffic simulation was carried out in the Zhengfeng No.2 tunnel of the S55 N ingxing Freeway in Ganzhou City,Jiangxi Province,and the simulation parameters were calib rated with the actual traffic characteristics data measured on site.In order to simulate the simu lation scenario more truly,Visual Studio 2019 software is used to complete the secondary dev elopment of COM interface of VISSIM traffic simulation software with C# language.Three e valuation indexes were calculated from the simulation output results,and the safe running spe ed under the constraints of evaluation indexes was obtained by CRITIC method and weighted average.By comparing the safe operating speed under the evaluation index constraint and line ar constraint,and considering the coordination of safety,efficiency and speed limit value,the speed limit value of small passenger cars and large trucks in Zhengfeng 2 tunnel is 80km/h.T he speed limit value for Zhengfeng Tunnel No.2 is calculated by comparing the method of de termining the speed limit value in the specification,and the result is far from the exact speed l imit value,which further verifies the scientific and applicability of the method in this paper.T he research results of this paper can provide new ideas for the formulation of safe operating sp eeds in freeway tunnels,which is of great significance for improving traffic safety and enhanc ing the efficiency of freeway tunnels. |
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