In the years to come, public transport will be called to play a significant role in achieving a sustainable transport system. To this end, the quality, accessibility and reliability of its operations should be improved. In this context, the favourable treatment of public transport means within the road network may have, among others, a significant contribution. Such treatment can be derived as a result of an appropriate design of the road network facilities and/or the employed signal control at the network junctions. PTPrealtime focuses on this latter approach aiming at developing methodologies for the favourable treatment, in real time, of public transport vehicles approaching signal controlled junctions.
Review the state-of-the-art and -practice of public transport priority strategies to identify the current trends and future perspectives in the field.
Develop a methodology and the corresponding software to provide public transport priority in real time, for public transport vehicles approaching junctions with relatively low frequencies.
Investigate the case of multiple public transport priority requests, i.e. when several public transport lines from different directions intersect at the same junction, and develop corresponding priority methodologies.
Investigate the effectiveness of the developed methodologies in public transport, and their implications to the rest of the traffic through microscopic simulations of an existing network using real traffic data.
PTPrealtime comprises six work packages:
- Review of literature and practical applications
- Development of a methodology and corresponding software for public transport priority provision in case of low frequency public transport operations
- Simulation evaluation of the methodology for the low frequency public transport operations
- Development of a methodology and corresponding software for public transport priority provision in the case of multiple priority requests
- Simulation evaluation of the methodology for multiple priority requests
- Dissemination and exploitation of the project results
The current state of practice, as identified through extensive literature review, indicated that the measures, which may be used to improve the performance of Public Transport Means (PTMs), fall into two general categories: (i) Facility-design-based measures and (ii) Signal-control-based measures. The later provide priority to PTMs based on predefined rules.
Two PTP methodologies of a rule-based nature were developed:
- The first methodology responds to infrequent priority requests via green extension or stage recall, without affecting the rules of road safety. In case of more than one priority request at the same junction and within the same period, a FIFO policy is applied, unless a subsequent request can be served by the same stage via a further green extension.
- The second methodology responds to multiple and conflicting priority requests. According to this methodology, in the case that two buses approach a signalised junction within the same cycle from conflicting directions, ask for priority treatment, one of the following cases can be followed:
- Case 1: The methodology developed for infrequent priority requests is applied for both buses. This, however, bears the risk that the second priority request may destroy the priority granted to the first bus. In general, the first bus that is detected is the one that will be served first. However, if during this period a second bus requests priority then the signal plan will change again and a new priority plan will be applied.
- Case 2: The second priority request will be served only if the first bus has crossed the junction. To make sure that the first bus has crossed the junction, extra detectors are placed at the exit of the junction, at the beginning of the downstream link. This approach eliminates the risk to destroy the priority granted to the first bus.
- Case 3: As in Case 2, the second priority request will be served only if the first bus has crossed the junction. Now, however, some extra detectors are placed between the entrance and exit detectors of the link to track again the position of the second bus at a later time, and reconsider it for priority provision, if at this later time the service of the first bus has been completed. These extra detectors serve one more purpose; they are used to update the bus travel time estimates and give a new more suitable priority plan.
Both methodologies were implemented in a microscopic simulation environment emulating the urban road network of the city of Chania, Greece, and tested under several scenarios of traffic conditions and priority requests. The performance of the methodologies was evaluated on the basis of mean delay, mean speed and total travel time (TTT), which were calculated both for the PT and private vehicles.
The pilot results indicated that depending on the traffic load and the frequency of receipt of priority requests, the mean delay and TTT of the PT vehicles could be reduced up to 32% and 15%, respectively, with an increase of mean speed up to 17%. At the same time, the effects to the rest of the traffic were found to be very limited.