The Capacity And Improvement Research On Urban Roundabouts

In the main roads of urban transportation network numerous roundabouts for the past decade are built,which have played an important role in road traffic history. However,with the rapid increasing of road traffic flows,traffic efficiency of roundabout decrease greatly.There are two major kinds of ideas to improve its traffic capacity and make full use of its time and space resource. It is to add signal control for roundabout and to change roundabout to signal intersection. The former have been divided into two kinds by left turn control mode, the first is general signal control (only install single lamp on the entry direction of ring, taking simple two-phase control), the second is left two step signal control (install singlelamp on the entry direction of ring and run off direction of ring, Left turning vehicles were quadratic controlled by signal in the ring before run off the ring).As for the existing roundabout, along with the increase of traffic pressure, which method (add signal control for roundabout and to change roundabout to signal intersection) should be taken to solve the traffic congestion and jams. It is urgent to solve the problem. Based on the analysis of urban road traffic characteristics of various control mode of the roundabout, the paper has also done research to the capacity of roundabout and to space and time design of roundabout. And according to the geometric conditionts and traffic survey data of the existing roundabout ,using the formor analysis, the paper makes the control mode choice using the research results to the example roundabout. Three kind of control modes were used to calculate the roundabout of scheme, and evaluate the effect after improvement.