Traffic Characteristics of Fully Enclosed Bypass Areas of Reconstruction and Extension of Two-lane Highways

In order to study traffic characteristics of the S + straight-line section + S-type bypass area, S + S-type by-pass area, and convex bypass area in reconstruction and expansion of two-lane highways, a field study is carried out for collecting traffic volume data and statistically analyzing speed variation of the three bypass areas. Then, the free flow speed and actual capacity of the main sections of the detour areas are calculated, in accordance with the calibration of the speed-flow conic model, and a simulation study for the traffic conflicts in the detour areas is carried out using Vissim. Study results show that the traffic bottleneck sections of the S + straight-line section + S type and S + S type bypass area appear in the driving curve section, while the bottleneck section of the convex bypass area presents at the end of the warning area. The average speed of the bottleneck sections in the three types of bypass areas is about 70% lower than that of the normal upstream sections, and the traffic capacity is reduced by about 50%. There is little difference in the traffic conflicts among the three types of bypass areas at low-volume flow. When the flow increases to above 500 pcu/h, the degree of traffic conflicts in the convex bypass area is much more serious than that of the other two types. In terms of comprehensive capacity, traffic efficiency, and traffic safety level, S + straight line segment + S-type bypass area is found to be more suitable than the others.