Variabla hastighetsgränser för Stockholms motorvägsnät: effekter av alternativa algoritmer och möjligheter till styrning genom estimerade trafiktillstånd

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Joakim Ekström
David Gundlegård
Rasmus Ringdahl
Andreas Tapani

Variable speed limits are commonly used on Stockholm’s urban motorways, and it is part of the Stockholm Motorway Control System (MCS). The goal of today’s system is to reduce the risk of accidents during congested conditions, traffic jams etc. This is done by updating the speed limits shown on variable message signs based on a measured average speed at fixed detectors. As the demand for travel in Stockholm during peak-hours exceeds the available capacity in the road network, the need for an efficient traffic system is high. Variable speed limit systems have the possibility to contribute to increased efficiency, but since today’s system aims to increase safety, effects that lead to increased efficiency are limited. Further, in todays’ variable speed limit systems there are a large dependency of precise and available measurements from stationary detectors to be able to display speed limits that reflects the current traffic conditions. The purpose of this report is to investigate alternative control algorithms to decide on the variable speed limits to be displayed at variable message signs on the urban motorway of Stockholm.

The goal is to increase efficiency compared to today's system. Two different road stretches with different complexity and different traffic conditions, resulting in two different types of congestion, are studied. Thereby, the studied control algorithms on the two road stretches are chosen based on the possibility of solving a specific problematic traffic situation in the best way. Hence, the studied control algorithms might differ for the two road stretches. Furthermore, for one of the roads stretches it is investigated if estimation of the traffic state can be used as input to the control algorithm as a complement to missing and erogenous measurements from stationary detectors in order to improve the calculations of the variable speed limits. The control algorithms are evaluated with microscopic traffic simulation and the method developed in the project Mobile Millenium Stockholm (MMS), using a macroscopic traffic flow model together with a Kalman filter, is used for estimation of the traffic state.

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