Provide traffic signal priority for buses at intersections to improve regularity and maximise the running speed (and the efficiency) of bus services.
By using traffic signal priority cities can give buses priority at traffic intersections and improve schedule adherence, reliability, and speed at the same time. Journey time measurement in Swedish cities shows that up to 70-80 % of all bus journey delays within urban city centres are due to waiting time at traffic signals, if there is no priority.
Traffic light priority benefits
The public (e.g. a faster , more frequent and more reliable bus ride with better comfort and less pollution),
The authorities (e.g. lower costs, more passengers and more accurate data for bus schedule planning and better control with PT operators),
The operators (e.g. more passengers, lower fuel consumption, less stress for drivers, improved operational efficiency, lower operating costs and higher revenues).
There are strong reasons for public transport priority because the reliability of the service (e.g. at interchanges) is improved. So a missed connection between less frequent lines (caused by the lack of bus priority at traffic signals) may add 30 minutes to a public transport journey for the gain of just a few minutes for a private car.
Modern prioritisation systems are intelligent: priority is only given when needed. Bus detection is fundamental to any bus priority function. Earlier designs of fixed detectors had several technical shortcomings, not least a high need for maintenance and poor accuracy at detecting all buses.
Different ways of traffic light priority comprise:
Extensions: Where the ‘at green’ phase is extended to allow the priority vehicle through the junction.
Recalls: Where a stage giving green to the priority vehicle is brought in early.
Queue jumping: Where a special stage is triggered, giving priority vehicles a chance to start ahead of other traffic.
Queue management: Where a queue of traffic is cleared to allow the priority vehicle a clear run through the junction.
Triggering green waves: Where a progression through a series of junctions is triggered by the arrival of a priority vehicle. In the standard static traffic signal progression (green wave), traffic signals are set to turn green as a platoon of vehicles moves from signal to signal. In contrast, a dynamic system provides a green wave for a group of traffic signals and then the platoon is stopped. A dynamic system changes traffic signal status based on the traffic conditions, rather than remaining constant as does a static system.
It is possible to simulate traffic light priority by software simulation tools (e.g. the software product VISSIM distributed by PTV, Germany).
In order to achieve a significant effect, the traffic flowneeds to reach a certain point. Within smaller cities a balance needs to be struck between giving public transport priority and avoiding general traffic disruption.
Traffic light priority in isolation achieves very little. The benefits of traffic light priority for public transport are more effective when priority is implemented as part of a package of measures for a whole corridor or route.
Aalborg (Denmark): In Aalborg the urban buses are given priority in all intersections. Over the city as a whole all bus prioritisation is integrated in around 50 intersections.
Brest (France): The city recently renovated a 6.5km long major north-south axis, providing 2.45km of bus lane and traffic signal priority for buses at the 8 signalised junctions involved (before and after photos of the route can be seen at http://www.cub-brest.fr/axenordsud/travaux_realises.htm).
Brighton & Hove (UK): When determining the requirements for a Real-Time system the Local Authority established that the Bus Operator's first priority was traffic signal priority for late running buses, followed by automatic vehicle location for operational control, and then real-time information. This was turned into an output specification and the city council went out to tender for a large system on that basis.
Jönköping (Sweden): In Jönköping there is bus priority at 13 of the traffic signals along the bus route. The bus priority signal system detects all buses that pass by, and is therefore also connected to the real-time information system at bus stops.
Luleå (Sweden): In Luleå, there is bus priority at 26 of the traffic signals along the bus route. One kind of signal priority used in Luleå is the bus sluice. It helps buses to move on from the intersection ahead of the other traffic.