Development and Evaluation of Algorithm for Resolution of Conflicting Transit Signal Priority Requests

Abstract

The goal of this study was the development and evaluation of an algorithm for resolving conflicting requests for transit signal priority (TSP). This algorithm was designed to work with actual traffic controllers without the need for new hardware or software installations. The algorithm was tested in VISSIM microsimulation and ASC/3 software-in-the-loop controllers on an intersection that will be upgraded to serve two conflicting bus rapid transit (BRT) lines. The ASC/3 logic processor was used to control built-in TSPs in the case of conflicting requests and to develop custom-TSP strategies that would not rely on built-in TSP. Custom TSP provides a much higher level of TSP for transit vehicles than built-in TSP, and it creates opportunities for more adaptable TSP control. The results showed that the widely used first-come, first-served policy for resolution of conflicting TSP requests was not the best solution. Such a policy could perform worse than a policy that provided no priority. For the analyzed intersection, the first-come, first-served option even increased BRT delays by 13% more than did the no-TSP option. The presented algorithm can help resolve the problem of the conflicting TSP requests. The algorithm worked best when combined with several TSP strategies. For the custom-TSP strategies, the application of the algorithm reduced BRT delays by more than 30%, with minimal impact on vehicular traffic. The algorithm shows promising results, and with small upgrades, it can be applied to any type of TSP.

State‐of‐the‐art and ‐practice review of public transport priority strategies

“…Rule-based, mainly reactive priority logic is even embedded or custom developed (see e.g. [58,59]) into the new-generation signal controllers. It is also offered as complementary element of the well-known signal control strategies split cycle offset optimisation technique (SCOOT), Sydney coordinated adaptive traffic system (SCATS), realtime advanced priority and information delivery (RAPID), balancing adaptive network control method (BALANCE), microprocessor optimised vehicle actuation (MOVA), and traffic-responsive urban control (TUC): † SCOOT [60,61] grants priority according to a schedule-adherence condition, mainly via green extensions and stage recalls; recent versions allow also for stage skipping.…”

Optimizing Conflicting Transit Signal Priority Requests: Application to an Isolated Intersection

“…Kim et al (2012) proposed a priority-based rule that considered the total headway delay of buses applying for the same priority, and the processor selected the TSP action with the largest headway delay. Zlatkovic et al (2012) designed a rule-based algorithm to classify conflicting TSP calls on a case-by-case basis during each cycle in accordance with the current intersection operation.…”

Network-wide analysis and design of transit priority treatments

“…(Zlatkovic et al, 2012b, Zlatkovic et al, 2012a, Zlatkovic et al, 2013, (Stevanovic et al, 2011), (Kim and Rilett, 2005)). This is mainly due to the sensitivity of TSP efficiency to several parameters such as intersection layout, vehicular flow rates, bus headway, bus stop locations, and signal coordination (Ngan et al, 2004).…”

“…In these strategies, the first bus that requests priority will be granted and all the other requests will be ignored until the system is restored to its normal condition. Head et al (2006) and Zlatkovic et al (2012a) showed that this method is not an efficient TSP strategy and even may occasionally perform worse than a Non-TSP strategy. Head et al (2006) presented a decision model for bus priority handling of traffic signals.…”

“…Evaluation of the model using a microsimulation method confirmed its ability to perform better (in terms of minimizing total bus delays) than the prior methods. Zlatkovic et al (2012a) presented a new method to deal with conflicting Transit Signal Priority strategies at the intersection. The major difference between their presented method and the FIFS approach was that in their model once the first arrived bus left the intersection, granting priority for the second bus would be checked.…”