A Feedback-Based Approach for Mainstream Traffic Flow Control of Multiple Bottlenecks on Motorways Georgia-Roumpini Iordanidou, Ioannis Papamichail, Claudio Roncoli, Markos Papageorgiou Dynamic Systems and Simulation Laboratory, Technical University of Crete, 73100 Chania, Greece (Tel: +30-28210-37422; e-mail: <giordanidou, ipapa, croncoli, markos> @ dssl.tuc.gr) Abstract: Mainstream traffic flow control (MTFC) enabled via variable speed limits (VSLs) has been investigated in previous studies, utilizing various control strategies. In this paper a new feedback control strategy is proposed for MTFC enabled via VSLs, considering multiple bottleneck locations. Results are evaluated using a validated macroscopic model. The feedback concept is robust and can be immediately implemented in the field as it considers practical and safety constraints. Keywords: Feedback control, Mainstream traffic flow control, Multiple bottlenecks, Variable speed limits. 1. INTRODUCTION Congestion on motorways is a major community problem which leads to a sensible reduction of the motorway infrastructure capacity (Papageorgiou and Kotsialos, 2002). This reduction occurs during the peak periods, causing degradation in terms of travel times, traffic safety, fuel consumption, and environmental pollution. With the purpose of alleviating traffic congestion, various control strategies have been suggested. However, some of them face limitations; e.g., ramp metering suffers from the limited number of vehicles that can be stored while route guidance is most valuable under non-recurrent traffic congestion. Mainstream traffic flow control (MTFC) regulates the flow upstream of a bottleneck location in order to maximize throughput at the specific location. This control action has been proposed by Carlson et al. (2010a, b) and was shown to lead to a remarkable improvement of the traffic flow efficiency indicators. In early research, Gazis and Foote (1969) had proposed a traffic-responsive control system for a tunnel flow control. Real-time traffic measurements from the bottleneck location were used by the system to make decisions on the tunnel’s flow control. Crowley and Greenberg (1965) and Foote and Crowley (1967) suggested the first simple feedback control strategy, while Foote (1968) and Gazis and Foote (1969) proposed a more sophisticated heuristic feedback algorithm. Another MTFC-like system is the traffic-light based entrance control system of the San Francisco-Oakland Bay Bridge, which was introduced by McCalden (1984) and has been in operation for more than 35 years. The algorithm used (Chen et al., 1990) appears to have important similarities with the algorithm proposed by Spiliopoulou et al. (2010). Finally, some fix-time mainline strategies have been investigated by Jacobson and Landsman (1994), and Haboian (1995) using traffic lights as a new traffic management tool for motorways. So far, the use of traffic lights is generally not acceptable on motorways. As a result, researchers have considered MTFC enabled by use of Variable Speed Limits (VSLs) with various control strategies and traffic application settings. In the work by Carlson et al. (2010b), it has been shown that ramp- metering and MTFC can have a similar impact on bottleneck locations, while an optimal control problem has been proposed by Carlson et al. (2010a) showing the benefits of MTFC, applied to a large-scale motorway. It is obvious from these papers that MTFC applied upstream of an active bottleneck location is able to avoid the capacity drop. Nevertheless, the optimal control approach used may be cumbersome for use in real field implementation. Zhang et al. (2006) proposed an ALINEA-like feedback controller for MTFC, based on VSLs, and performed tests via microscopic simulation. The obtained improvements were marginal probably because of the absence of an acceleration area, as proposed by Carlson et al. (2010a, b). This paper proposes an extension of the feedback controller presented by Carlson et al. (2011) for the case of multiple bottlenecks. The issue of multiple bottlenecks was addressed by Wang et al. (2010) for the case of ramp metering control; hence this paper combines the concepts developed by Carlson et al. (2011) and Wang et al. (2010) to derive a feedback law for VSL-based MTFC addressing multiple downstream bottlenecks. The new feedback control strategy is simple and robust and can be directly applied in the field. Many practical aspects of VSL operations are also considered in the simulation-based tests using a validated second-order macroscopic traffic flow model. In Section 2, the MTFC concept is reviewed and the implementation aspects are presented. In Section 3, the MTFC strategy for multiple bottlenecks is described, taking into account practical application aspects. The efficiency of the proposed control strategy is evaluated in Section 4, while the conclusion of this paper and some ideas for further research on the subject are presented in Section 5. Preprints of the 19th World Congress The International Federation of Automatic Control Cape Town, South Africa. August 24-29, 2014 Copyright © 2014 IFAC 11344