双车道公路改扩建全封闭绕行区交通特性

针对双车道公路改扩建中的S+直线段+S形绕行区、S+S形绕行区以及凸形绕行区，基于现场交通流参数调查与数据处理，统计分析了3类全封闭施工绕行区的车速变化特征，标定了速度-流量二次曲线模型并据此计算得到了绕行区各主要区段的自由流速度和实际通行能力值，采用Vissim仿真软件进行了绕行区的交通冲突仿真实验。研究结果表明:S+直线段+S形及S+S形绕行区的交通瓶颈路段均出现在驶入曲线段，凸形绕行区的瓶颈路段则出现在警告区末端。3类绕行区瓶颈路段的平均速度较上游正常路段降低了70%左右，通行能力则降低了50%左右。在交通冲突方面，在低流量时3类绕行区的交通冲突情况差异不大，当流量增大到500 pcu/h以上时，凸形绕行区的交通冲突明显比其他2类绕行区更为严重；综合通行能力、通行效率及交通安全水平3个方面，S+直线段+S形绕行区是1种比较适宜的绕行区形式。 

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.