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Traffic light priority systems
Traffic light priority systems
Reliability of public transport systems is considered critically important by public transport users, operators and public authorities. Lack of reliability and schedule adherence result in increasing anxiety and discomfort for passengers, which will eventually lead to a lower use of public transport services.
In highly congested cities, during peak hours or under any other heavy traffic conditions, general traffic has a great impact on public transport reliability. Among the different initiatives studied by transport authorities to reduce that impact, there are solutions such as dedicated bus lines or traffic light priority systems. This article will focus on the latter.
Traffic light priority systems (TLPS) are designed with the objective of giving green-light priority to public buses approaching a junction. A TLPS will require an exchange of information between the bus Fleet Management System (FMS) and the Traffic System used in the city or geographical area. Once the communication has been established between these systems, the FMS will issue priority requests, either from the servers or directly from the vehicles; once those requests have been received at the traffic system, the Traffic Controller will evaluate them and decide whether to service the request and give the bus a green light or keep the planned traffic-light cycle.
There are different ways of implementing a traffic priority system but they all share a set of requirements that need to be met:
- Schedule adherence assessment, we do not want to issue a priority request if the bus is on time or ahead of schedule. Additionally, some managers would also not want to issue a request when the bus is running very late, as it wouldn’t make much difference and the bus would still be behind schedule. This schedule adherence assessment can only be performed by means of an advanced Fleet Management System.
- Junction detections, the detection of arrival at a junction is a vital point in terms of issuing the request whenever it is needed. These detections might be software based and performed by the bus on-board unit or they might be a combination of sensors installed on the road and in the bus. How to perform these detections is probably the key point when deciding on the design of the Traffic Light Priority System. This choice will have an impact on the cost and complexity of the project implementation as well as on the accuracy of the final system.
Once the entrance to a junction has been detected, the request should also indicate the desired exit of the junction, as most of the crossroads will have different directions.
- Priority Request assessment. The Fleet Management System will not have information on the real-time status of general traffic. Therefore, the only assessment it will make will be regarding the different priority-requesting buses . In the scenario of two different buses arriving at the same junction and both running behind schedule, it will decide which of the bus-priority requests is finally sent to the traffic system.
The next step, once a priority request has been received at the Traffic System, is for the Traffic System to decide whether or notthat request should be met. In the situation of a junction close to an important station, it would be possible to receive priority requests every minute from different buses, which could eventually have a great impact on the other traffic directions.
Traffic Light Priority systems for public buses are a very interesting initiative to be evaluated by Transport Operators and Authorities. They can improve travel time reliability, thereby increasing Public Transport attractiveness as compared to private vehicles.
Author: Ahmad Kamal Haridan Jajuli