On the control of left-turning traffic

The objective of this analysis is to determine a method for controlling left-turning traffic while minimizing the total delay in the intersection. A left-turn may be performed using a left-turn phase or an uncontrolled turn. When a controlled left-turn phase is used, a special turning phase is given to the turning stream, resulting in some delay to the turning vehicles and an increased delay to the other traffic streams in the intersection. The delay in this case can be found using the results given by Webster [1]. On the other hand, if an uncontrolled left-turn is performed, the opposing on-going stream is given the right-of-way while the turning vehicles may turn only if an acceptable gap in the opposing stream occurs. Consequently, the turning vehicles form a queue while waiting for an opportunity to turn. Note that in this case the turning vehicles do not add to the delay of other traffic streams and they cause only the delay incurred by themselves. Thus, in order to compare the delay caused by left-turning vehicles under the two methods, it is necessary to find the delay caused to the left-turning stream under an uncontrolled turn.