A Cooperative Control Method of Variable Speed Limit and Lane Change for Mixed Traffic Flow on Continuous Bottlenecks of Freeway

A cooperative control method of variable speed limit and lane change for mixed traffic flow consisting traditional human-driven vehicles and connected and connected and automated vehicles (CAVs) is developed to mitigate the capacity drop due to mandatory lane change and mutual interference between bottlenecks in the freeway. The traditional cell transmission model (CTM) is modified to better predict the mixed traffic flow state under variable speed limit control. A reasonable length of lane change section under different traffic demands are then obtained using experimental simulation. The capacity drop due to mandatory lane change is alleviated by reminding the drivers of upstream vehicles. In this way, the performance for variable speed limit is improved. Meanwhile, variable speed limit is adopted to regulate high traffic demand for the vehicle to successfully change lane. The cooperative control framework is set up for continuous bottlenecks, where the traffic performance is optimized by minimizing the total travel time and speed difference. At last, different penetration rates of CAVs' impact on cooperative control is analyzed. Study results show that, compared to the results of no-control or only variable speed limit, the total travel time with cooperative control, respectively is reduced by 54.76% or 33.05%, and the total speed difference is reduced by 86.84% and 29.58%, respectively. In addition, study results also show that the penetration rate of CAVs has a positive impact on the performance of cooperative control and traffic operation: if the penetration rate increased from 0 to 0.5, the minimum speed limit can be increased from 30 km/h to 60 km/h, while the speed limit value is kept as the free speed when the penetration rate reaches 1; the total travel time reduces from 239.64 h to 158.86 h with cooperative control in place as the CAVs penetration rate increases. This study provides a reference for the active control of continuous bottlenecks of freeway under a mixed traffic environment.