Traffic metering on on-ramps improves traffic operations on freeway facilities by maintaining traffic state in undersaturated flow conditions and avoiding capacity loss but, at the expense of delaying vehicles entering the freeway from on-ramps. The same concept offers great potential to improve traffic operations by regulating/limiting the flow of vehicles into congested areas of urban street networks. We have used the cell transmission model to construct a mathematical program to optimize metering rates in urban transportation networks. We use the Benders decomposition to convert this complex optimization program to a much simpler program and a bunch of simulation runs. Our simulation results showed between 5% to 8% improvement in network throughput as a result of optimal traffic metering. This improvement was achieved due to preventing spillovers and gridlock inside the network.
While the developed benders decomposition approach is quite efficient, it cannot find optimal metering rates in real-time. Therefore, we have developed a distributed model predictive control algorithm for traffic metering. The approach distributed the network spatially to several sub-networks and optimized metering rates in each of those in coordination with others. This approach finds optimal metering rates in real-time that are comparable to the solutions that are found by the Benders decomposition approach.
We are also working on cooperative traffic signal optimization and perimeter control. The main idea is to share information between the signal controller and perimeter controller such that they can work together. We developed a distributed optimization and coordination technique to find optimal solutions in real-time. Our simulation results show that the cooperative approach increases the number of completed trips by 6.0% – 12.8% and 10.9% – 11.0% and reduces the total travel times by 8.1% – 9.0% and 23.6% – 24.2% compared to independent signal control and independent perimeter control, respectively. Here are some of our publications on this topic:
- Mohebifard R.* and A. Hajbabaie, 2018. Dynamic Traffic Metering in Urban Street Networks: Formulation, Algorithm, and Application. Transportation Research Part C: Emerging Technologies, Vol. 93, pp 161-178.
- Mohebifard R.* and A. Hajbabaie, 2019. Distributed Optimization and Coordination Algorithms for Dynamic Traffic Metering in Connected Urban Street Networks. IEEE Transactions on Intelligent Transportation Systems, Vol. 20, No. 5, pp 1930-1941.
- Mohebifard R.*, S. Islam*, and A. Hajbabaie, 2019. Cooperative traffic signal and perimeter control in semi-connected urban-street networks. Transportation Research Part C: Emerging Technologies, Vol. 104, pp 408-427.