Implementing more adaptive signal control in a bus priority system

Summary

Increasing the reliability and attractiveness of Stockholm’s bus service and reducing queuing and pollution contributed to creating a more efficient and better used urban public transport system.

Implementing sustainable mobility

The timing of traffic light changes depends on complex decisions based on variations in traffic flow, traffic composition, dependency on neighbouring junctions and safety considerations. The support system must be modern, flexible and inexpensive to maintain and must be appropriate for the existing vehicle stock in the city.

In this technology assessment measure, a new, more adaptive traffic control system was tested in Stockholm in order to compare it with the system already in place. In the new SPOT/UTOPIA system, instead of pre-defined fixed time plans for the entire coordinated system, with only limited flexibility, a mathematical optimisation procedure is run repeatedly in order to identify the optimal time to change the colour of the traffic lights. This is done every third second. The hardware comprises an industrial PC card mounted with communication hardware in a box installed on top of the existing controller inside the signal controller cabinet, one at each intersection. Communication wiring between units and a central computer are also installed. This allows for convenient system monitoring using standard PCs and modern communication technology.

The new adaptive system was installed in parallel with the existing fixed-time system at 11 intersections within a test area. Over a number of days in May 2003, the two systems were in operation alternately. The situation before and after was measured according to a defined evaluation plan, which was complemented by performance indicators specific to the local road authorities.

Progress

The steps included:

• planning, software programming, equipment procurement, installation and tuning during 2002;
• system checks and assessment issues during spring 2003, with the trial taking place in May;
• installation and testing of the “public transport locator”, a feature within the SPOT/UTOPIA framework, identification of the key indicators needed for the final evaluation of the project, and development of a simulation-based method for their estimation; and
• preparation of a report on the effects of the dynamic bus priority weighting system.

Outcomes

Stockholm did not proceed with installation of the SPOT/UTOPIA system due to concerns that it was not adapted to Swedish needs, particularly with regard to pedestrians and cyclists. Instead, Stockholm worked to optimise traffic signals in the framework of the city’s MATSIS project (“Reduced CO2 Emissions through Adaptive Traffic Signalling in Stockholm”), focusing on coordinating advanced but standard methods of Swedish signal control techniques, including a number of adaptive solutions to simulate carbon dioxide, local emissions and fuel consumption during the start/stop phases. The results were very good, with delay times substantially reduced. MATSIS became one of the most profitable environmental projects carried out by the city of Stockholm.