Arterial Signal Coordination Considering the Impacts of Left-Turn Waiting Areas

Abstract

The left-turn waiting area (LTWA) has been commonly used in many signalized intersections to increase the capacity of left-turn movements. However, LTWAs may negatively affect the performance of arterial signal coordination because the lag-lag left-turn phase sequence turns out to be the only feasible left-turn treatment to accommodate the presence of LTWAs. To investigate the effects of LTWAs on arterial signal coordination, this paper proposes an analytical model based on the classic MAXBAND algorithm to quantify the gaps between the actual bandwidth and the maximum possible bandwidth. The model can further identify the applicable signal timing condition of LTWAs in an arterial signal system. A case study of a signalized arterial with LTWAs in Wuhan City was conducted to verify the effectiveness of the proposed method. Results showed that the signal timing parameters obtained from the proposed model resulted in a shorter queue length, a lower delay, and a smaller number of stops when the lag-lag phase sequence was adopted in comparison with the other phase sequences. The left-turn waiting area (LTWA) has been adopted in many cities to improve operational efficiency for turning traffic, especially for large intersections. However, a lag-lag phase sequence has to be adopted at signalized intersections with LTWA, which would affect the performance of arterial coordination due to the limitations of the phase sequence. The model proposed in this paper could assist field engineers with exploring the appropriate signal timing condition for an arterial coordination system with LTWA intersections, where the lag-lag left-turn phasing scheme could produce wider bandwidth than the other phase sequences. In addition, the rationality of LTWAs in an arterial system could be evaluated further according to the real traffic situation.