To evaluate the environmental benefits and operating efficiency of exit lanes for left-turn intersections, a signal optimization model considering emissions and delays is proposed. Considering the three pollutants of CO, HC, and NOx in cars and buses exhaust, VISSIM simulation software is used to obtain second-by-second data of vehicles. The data is used to calculate the second-by-second Vehicle Specific Power and to calibrate the two types of emission factors for each lane group. Cycle length, main-signal and pre-signal control are regarded as constraints, and minimum emissions and delays are regarded as optimization goals. The bi-objective optimization for exit lanes for left-turn intersections is transformed into a single-objective optimization problem through the linear weighted sum method, and the genetic algorithm is used to solve the optimal signal timing scheme. The results show that, compared with conventional intersections, the design of EFL intersections can not only improve operation efficiency, but also reduce emissions. The optimal signal timing scheme for exit lanes for left-turn intersection can reduce the delay by 6.27% and the total emissions by 7.47%; At the same time, when the proportion of left-turn traffic is 35%~40%, the signal optimization model proposed in this paper has the best optimization performance. Effective in relieving traffic pressure and has good environmental benefits.
For a long time, the operation efficiency of highways in Sichuan plateau mountainous areas has been low, and overtaking accidents occur frequently. In addition, many places are limited by natural conditions and unable to build the two-way four-lane highway. Hence, this paper proposes a new scheme to transform and expand the two-lane road into a 2+1 alternate lane. We used VISSIM software, combined with the actual traffic characteristics of the Sichuan mountainous area, and integrated with the driving behavior features to conduct a simulation analysis on the geometric parameter design, setting influencing factors and applicability of 2+1 alternate highway. It not only fills the domestic research gap but also provides theoretical support for building a safe and efficient mountain traffic system. The study found: This scheme optimizes the service level while improving the operation efficiency. When the proportion of trucks exceeds 20%, prohibiting trucks from passing through overtaking lanes shows relatively higher service levels. 2+1 alternate highways in mountainous areas have significantly better service levels than other options when the overtaking lane length is set to 550-900m, and the speed limit in the single lane is 50-100km/h.
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