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Public transport priority at intersections

Ljubljana

Ljubljana is eager to build up a bus network that provides a fast, convenient and energy-efficient way to get around the city. The municipality hopes that this attractive offer will lead more people to use public transport instead of the private car. One of the measures leading to this goal is the implementation of public transport priority at intersections.

Implementing sustainable mobility

Congestion is slowing down traffic in the city centre of Ljubljana where the average speed ranges between 10 and 18 km/h. Public transport prioritisation has successfully improved traffic flow and the speed of the public transport service in cities across Europe. Traffic light priority has for example led to average time savings of around 20 percent per bus in several cities. Ljubljana followed this example and drew on national and European research in the field of prioritisation of public transport and also by equipped the city buses with adequate technology that enables it.

The main objectives of the measure were to:

  • Equip buses and intersections with the technology that will enable direct communication between the PT fleet and the infrastructure, and furthermore
  • Increase the speed of the public transport bus service and decrease idling;
  • Offer a more user-friendly service for commuters, more effective and less time consuming service for everyday mobility needs; and
  • Attract more passengers to the bus service.

Ljubljana used statistical models and a traffic light priority scheme to improve the performance of the bus service. Selected intersections in the city are equipped with technology to enable direct signals from the public transport fleet to be sent to traffic lights. The equipment is fully compatible with Galileo satellite navigation to allow for easy upgrades of services once the system becomes available. Ljubljana has been running a pilot project on traffic light prioritisation that helped to define issues and solutions in the planning and preparation phase of the measure.

How did the measure progress?

Ljubljana has acquired a direct communication technology called Zigbee for 210 buses and 15 intersections which enables traffic light operators to adjust the traffic light regime (extend or shorten interval) when a bus is in the proximity of a traffic light and thus provide public transit priority.Systems have been upgraded to integrate this new technology. The municipality has undertaken scenario modelling based on bus tracking and statistical data. It has also introduced encrypted communication to prevent abuse of the system.

What were the outcomes of the measure?

The key results show the following:

  • The average ratio between the number of sent information packages arrival / departure event vs. acknowledgment (ACK) packages (ACK packages indicate the request for public transit priority was received and triggering executed (i.e. green light interval extended for the PT) shows a very high level of system performance. Over 95% of tested traffic light triggering operations have been successful. The target values have been exceeded. However, this is only the technological aspect of the measure – to achieve significant impact in regard with the transport parameters, the system will have to be optimised (implementation of the PT priority system throughout the corridor/city).
  • The results show a significant improvement in accuracy of arrivals. Since the data on travel speed and travel times remains relatively constant (almost no impact is evident), this can be attributed to the location of bus stops in a relation to the location of PT priority intersections. Since the traffic light priority (TLP) installed intersections are scattered, this could result that the punctuality is increased on those bus stops, which improves the general schedule adherence. It could be stated, that the target levels have been achieved in full.
  • The PT operator (LPP) has already recognized the importance of this feature and included it in its future strategy. The measure has become part of the City’s “Transport Policy Proposal until 2020”, to be a part of other newly established integrated high-quality mobility corridors.

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