Next generation motorway traffic control

Motorway traffic control is an important element in today’s traffic system and especially at urban motorways that is connecting the city central to suburbs and acting as a thoroughfare for traffic passing the city. Variable speed limits are one of the most common control strategies in the existing Motorway Control System (MCS) currently implemented in Stockholm. In the system, a control algorithm is used to find the speed limit to be displayed on variable message signs. The goal is to warn the drivers about incidents and thereby improve the traffic conditions when an incident has already occurred by lowering the speed limits. Hence, the focus has been to improve safety. However, there is also a potential to improve the traffic performance, such as reduced travel times and increased speeds, by applying a control algorithm with focus on traffic efficiency. In this case the speed limit is reduced at traffic flows close to the capacity to homogenizes the speeds and reduce instabilities in order to delay or even avoid a traffic flow breakdown.

A high compliance level, as well as a control algorithm adapted to the specific traffic condition and road design, are required to have a good performance of the variable speed limit system. In Stockholm the displayed speed limits has up until now only been recommended, sometimes resulting in a low compliance level. However, the Swedish Road Administration is currently developing their MCS by introducing mandatory speed limits. They also investigates the possibility to implement a more flexible system with the opportunity to apply different control algorithms depending on the traffic conditions at specific locations.

In this project, the overall goal is to support the Swedish Road Administration in the implementation of the development of the MCS in Stockholm. The aim is to investigate how new control algorithms for variable speed limits can be introduced in the MCS by automatically control the speed limits. One important aspect to investigate is how the control algorithms should be designed and described to comply with the rules and legislations in Sweden when assuming mandatory speed limits. Further, the possibility to more effective traffic control through the use of vehicle data and implementation of variable speed limits in combination with control strategies that aims to decrease effects of a capacity reduction due to lane-changes at critical locations is investigated.
The project is carried out in collaboration between VTI and LiU and is funded by Trafikverket via Centre for Traffic Research (CTR).