Research On Speed Limit Of The Reconstruction And Expansion Expressway Without Interrupting Traffic

As some of the expressways built in the early days have problems such as insufficient capacity and reduced service levels,the reconstruction and expansion of expressways will continue for a period of time in the field of transportation infrastructure construction.In order to reduce the pressure on the surrounding traffic as much as possible,many expressways choose construction methods that do not interrupt traffic.During the reconstruction and expansion,construction and opening to traffic are carried out at the same time,and it is necessary to ensure the safety of driving and construction through reasonable traffic organization.According to the characteristics of different stages of construction,the scientific and reasonable speed limit management of the traffic flow is helpful to improve the traffic efficiency under the premise of ensuring the safety of the vehicle operation.And it is also one of the important issues to be studied in the expressway reconstruction and expansion project.Based on micro-simulation technology and safety conflict theory,this paper studies the speed limit problem of expressway reconstruction and expansion for uninterrupted traffic.Relying on the actual project investigation,the construction phase division and the corresponding traffic organization phase division of the reconstruction and expansion expressway without interruption of traffic were obtained.The characteristics of the traffic flow in different stages were investigated to obtain the characteristic data such as traffic volume distribution,vehicle type distribution,vehicle speed distribution and operating speeds of different locations during the reconstruction and expansion of the expressway.After comparison,it was found that the vehicle composition and speed characteristics during the reconstruction and expansion are very different from those before the reconstruction and expansion.And the bottleneck section is mainly the opening section of central divider caused by asynchronous construction.On this basis,the sensitivity analysis of the microscopic parameters of the simulation model was carried out,and it was found that the model calibration result was most effective when the flow rate was used as the calibration index.And based on this,the simulation basic model was calibrated.The basic road section and the opening section of central divider of traffic flow during the reconstruction and expansion are selected as the object of the speed limit study.Aiming at the different stages of traffic organization during the reconstruction and expansion period,the types of basic road sections and the types and length ranges of opening sections of central divider were analyzed.And based on VISSIM simulation and basic capacity correction,the capacity of different types of road sections is obtained.Consider the three road saturation levels of low,medium and high.The VISSIM simulation was used to analyze the sensitivity of the traffic composition and the length of the opening section of central divider.It was found that there is no significant difference in safety when the gap between the length of the opening section of central divider is less than 100 m,and the more appropriate limit rate for big trucks during the reconstruction and expansion period is 10%.Based on the above analysis,a simulation plan for basic section and opening section of central divider speed limit research was developed,with safety,stability,traffic efficiency,fuel economy as evaluation indicators,and TOPSIS method as the comprehensive evaluation method.Through the simulation research on the speed limit strategy of the basic section of single lane and double lane,after comprehensive evaluation,it was found that the optimal speed limit of the basic road section is 80km/h.Based on the measured 85% speed,it is recommended to limit the speed of the basic road section to 80 km/h during the reconstruction and expansion of the expressway.Based on the recommended speed limit value of the basic road sections,different speed limit schemes for the opening section of central divider were studied,and no significant differences were found between the 10km/h and 20km/h speed limit tier values and the 100 m and 200 m tier distances.Various simulation strategies for different types of opening section of central divider were simulated to obtain evaluation indexes.The comprehensive evaluation results indicate that the theoretical optimal speed limit scheme suitable for all types of pening section of central divider is 70km/h,which is set at 1/2 of the warning zone.This optimal solution is suitable for ideal road conditions,and is the maximum speed limit value of the opening section of central divider.In actual application,specific road conditions can be considered to reduce the final speed limit value to 60km/h or 50km/h.