Optimization model for bus priority control considering carbon emissions

Two bus signal priority control strategies - green extension and red truncation - were studied.Carbon emission and delay calculation methods under the bus priority control were developed.Considering carbon-emission reductions of buses and social vehicles with different fuel types under different working conditions.Three control methods were studied: guidance acceleration, guidance acceleration and green extension, and guidance deceleration and red truncation. To study the impact of bus priority control (BPC) on traffic carbon emissions under the strategies of speed guidance, green extension (GE), and red truncation (RT), with consideration of the main influencing factors such as delay, stopping times, and speed, a combination optimization method was used to develop a bi-level optimization model for BPC. The optimal carbon-emission reductions of buses and social vehicles with different fuel types in the upstream section of the intersection and the intersection control area was the upper-level objective, and the optimal total passenger-delay reduction was the lower-level objective. The Gauss - Seidel iterative algorithm was used to solve the model. Finally, the model was applied to the analysis of calculation cases. The results indicated that after BPC was adopted under the guidance acceleration strategy, the reductions in the carbon emissions and total delay of passenger were optimal when the guidance speed was 38 km/h, i.e. 12.67% and 21.05%, respectively. Under the guidance acceleration and GE strategy, the reductions in the carbon emissions and total delay of passenger were optimal when the guidance speed was 39 km/h and the GE was 6 s, i.e. 27.49% and 38.62%, respectively. Under the guidance deceleration and RT strategy, the reductions in the carbon emissions and total delay of passenger were optimal when the guidance speed was 29 km/h and the RT was 6 s, i.e. 22.18% and 33.52%, respectively. The model reduced the carbon emissions and total delay of passenger in the upstream section of the intersection and the intersection control area to achieve the optimal overall traffic benefit for the intersection.