ADAPTIVE COORDINATED TRAFFIC CONTROL FOR STOCHASTIC DEMAND
Pacific Southwest Region University Transportation Center
Traffic arrivals at intersections are inherently uncertain due to variable traffic conditions. This paper develops an adaptive coordinated traffic control approach via the notion of Phase Clearance Reliability (PCR) (Lo, 2006). In contrast with a conventional green extension scheme, the proposed approach adjusts signal offsets adaptively to explicitly address the presence of stochastic demands. Based on the cumulative queuing regime, we first extend the delay models, which are usually formulated for isolated intersections, to coordinated intersections by incorporating the effects of residual queue and signal offset. We then formulate a two-stage stochastic program to minimize the expected total delay for the coordinated corridor. The base timing plan is derived at Stage 1, while recourse decisions of adaptive signal offsets are made at Stage 2 to compensate for the overflow effects. Furthermore, a PCR-based gradient solution algorithm is developed to solve this two-stage stochastic program. The case study on a 3-intersection network under different levels of demand variability confirms the effectiveness of the proposed PCR-based control method, which can reduce the expected total delay by as much as 50-60% compared with the traditional optimization approach, as confirmed by simulation with the Cell Transmission Model. Its remarkable performance stems in a large part from the resultant much shorter cycles, as the random arrivals are addressed by adjusting the signal offsets adaptively. This effective use of signal offset provides a new perspective for designing coordinated signal control plans.
Professor Hong K. LO is Department Head and Chair Professor of Civil and Environmental Engineering and Director of GREAT Smart Cities Center of the Hong Kong University of Science and Technology. His expertise includes dynamic transportation system modeling, traffic control, network reliability, and public transportation analysis. Professor Lo is very active in the transportation community, for instance, elected as Convener of the International Scientific Committee of the conference series Advanced Systems for Public Transportation (CASPT), serves as Founding Editor-in-Chief of Transportmetrica B: Transport Dynamics, Managing Editor of Journal of Intelligent Transportation Systems, and on the editorial boards of many international journals, including Transportation Research Part B, International Journal of Sustainable Transportation, ASCE Journal of Urban Planning and Development, among others. Professor Lo was awarded the prestigious triennial World Conference on Transportation Research (WCTR) Prize in 2001, Eastern Asia Society for Transportation Studies (EASTS) Outstanding Paper Award in 2003, and Hong Kong Institution of Engineers (HKIE) Transactions Prize in 2000, more recently, HKUST School of Engineering Research Excellence Award in 2014. Prof Lo is a Fellow of The Hong Kong Institution of Engineers (HKIE), Fellow of the Chartered Institute of Logistics and Transport (CILT), Fellow of the Hong Kong Institute of Highway and Transportation (IHT), and Fellow of the Hong Kong Society for Transportation Studies.