**2. Transit signal priority tactics**

The goal of all tactics is to grant green time when transit vehicles are approaching intersections, which would offer them shorter delays. To do so, a combination of TSP tactics is given the best result. Thus far, a lot of tactics have been used; most of them are listed below.

**185**

return [17, 18], etc.

*Transit Signal Priority in Smart Cities*

detected will be measured [10].

interruptible bus requests.

a major bus terminal [9].

queues measured by the 35th percentile.

is ineffective where bus volume is high [9].

*DOI: http://dx.doi.org/10.5772/intechopen.94742*

few seconds after the end of green time, which opens a short green-window for the transit vehicle. It provides a relatively large bus delay-reduction, but only for a small fraction of busses that arrive at the signals approximately the end of green phase [8, 9]. The maximum green extension is an input value in the TSP logic. Based on that, and together with bus speed, a maximum point/time at which transit can be

*Early Red or Green Truncation* is another main TSP tactic scheme that has been widely implemented. It is granted to accommodate transit vehicle that would arrive a few seconds before the start of green. Green truncation cuts down the green time of the conflicting or non-transit phases so that the signal cycles faster and provides a green window sooner to the transit vehicle that stopped behind the traffic lights. This tactic serves all busses caught at red light, providing a small benefit to many [8, 9]. Since the early red technique cuts down the green of the conflicting phases, while there are vehicles in the queue, it causes greater disruption to the conflicting traffic and it is recommended to be applied to intersections with low to medium

*Phase Rotation* is a TSP technique that has been recently emerged in studies. It changes the sequence of the phases in the ring barrier signal system to match the bus's arrival time with the green light. It mostly changes a leading left phase to a lagging left phase or vice versa. Thus, the application of phase rotation tactic comes into play when there is a left-turn phase in the ring barrier with more than two critical phases. For example, it assumes that the initial signal timing design is set to be leading left and lagging through. Assuming that the bus runs in the through-phase, the phase rotation tactic changes the sequence of the phase in such a way as to make the through-phase lead and the left-turn phase lagged. The effect of phase rotation

*Phase Insertion* is another tactic used to provide green time for transit vehicles. This tactic strategy is applied mostly when there are several turning movement phases, and the logic is not flexible enough to handle such a case when the transit vehicle arrives in the middle of a red light, making the logic unable to apply other TSP techniques like Green Extension or Early Green. Instead, it creates a temporary green phase within a cycle. Sometimes it is called Double Realization because the transit-phase receives green time twice in one cycle. Double realization is used for a left-turn phase at an intersection with high bus requests [9]. The phase sequence used was leading left - through movement - lagging left (for the second time), which all were applied in one cycle, at a signalized intersection near

*Queue Jump* is another transit preferential treatment that stretches a short buslane at traffic signals, together with a specific queue jumper leading phase interval. This allows busses to receive green light sooner in order to be ahead of the queues backed-up in the adjacent lanes [11]. Queue jump was applied in a few studies and the results have shown that the combination of queue jump treatment and signal priority tactics have yielded the highest benefit in terms of transit travel time, speed, and delay as compared to scenarios in which each one is deployed separately [12, 13]. Cesme and Altun [14] studied the effect of queue jump lane on a hypothetical intersection. The results revealed that a queue jump lane corresponding to the 95th percentile queue has reduced the transit delay 1.3 times more than that of

There are other transit signal tactics that have been introduced, which in a sense is the combination of the above listed tactics; some of which include: transit phase truncation and queue dissipation [15], early red, flush-and-return [16], expedited

*Green Extension* is one of the main TSP tactics that has been used in most TSP studies. It extends the green time when the transit vehicle is expected to arrive a

### *Transit Signal Priority in Smart Cities DOI: http://dx.doi.org/10.5772/intechopen.94742*

*Models and Technologies for Smart, Sustainable and Safe Transportation Systems*

either busses, tramways, or streetcars, through signalized intersections without the interruption of red signal lights when possible (see **Figure 1**). It can be an effective strategy for lowering transit vehicle delays at signalized intersections as well as passengers delays, reducing fuel consumption and vehicle emissions, preventing bus-bunching, and significantly enhancing transit reliability which results in transit with lower passenger waiting time and operating costs (smaller transit fleet size). The Transit Capacity and Quality of Service Manual [2] described bus preferential treatments at intersections including transit signal priority, queue jumping, curb extension, and boarding islands. Among the stated transit treatments, TSP has the lowest cost and can easily be implemented in dense urban transportation networks, while other treatments require more capital and physical spaces to be considered. In practice, transit agencies are more interested in making use of limited resources in an efficient manner and TSP could satisfy such needs. However, the impact of TSP will prove more effective with the use of extensive evaluation, ongoing performance monitoring, and adjustment after the initial implementation [3]. By 2015 [4], 109 cities around the world, mostly in North America and Europe, have implemented TSP. However, the majority of attempts used simple and easy-to-implement logics in practice. Portland, Los Angeles, Chicago, and New York City in the United States have been the pioneer cities in implementing TSP in order to enhance their transit system. Various technologies have been deployed for TSP including: the Loopcom System in Los Angeles, CA, the Amtech System in Seattle, WA, the TriMet in Portland, OR, and wireless local area network in Minnesota, MN and in New York City, NY [5–7].

The goal of all tactics is to grant green time when transit vehicles are approaching intersections, which would offer them shorter delays. To do so, a combination of TSP tactics is given the best result. Thus far, a lot of tactics have been used; most of

*Green Extension* is one of the main TSP tactics that has been used in most TSP studies. It extends the green time when the transit vehicle is expected to arrive a

**184**

**Figure 1.**

*Transit signal priority framework.*

**2. Transit signal priority tactics**

them are listed below.

few seconds after the end of green time, which opens a short green-window for the transit vehicle. It provides a relatively large bus delay-reduction, but only for a small fraction of busses that arrive at the signals approximately the end of green phase [8, 9]. The maximum green extension is an input value in the TSP logic. Based on that, and together with bus speed, a maximum point/time at which transit can be detected will be measured [10].

*Early Red or Green Truncation* is another main TSP tactic scheme that has been widely implemented. It is granted to accommodate transit vehicle that would arrive a few seconds before the start of green. Green truncation cuts down the green time of the conflicting or non-transit phases so that the signal cycles faster and provides a green window sooner to the transit vehicle that stopped behind the traffic lights. This tactic serves all busses caught at red light, providing a small benefit to many [8, 9]. Since the early red technique cuts down the green of the conflicting phases, while there are vehicles in the queue, it causes greater disruption to the conflicting traffic and it is recommended to be applied to intersections with low to medium interruptible bus requests.

*Phase Rotation* is a TSP technique that has been recently emerged in studies. It changes the sequence of the phases in the ring barrier signal system to match the bus's arrival time with the green light. It mostly changes a leading left phase to a lagging left phase or vice versa. Thus, the application of phase rotation tactic comes into play when there is a left-turn phase in the ring barrier with more than two critical phases. For example, it assumes that the initial signal timing design is set to be leading left and lagging through. Assuming that the bus runs in the through-phase, the phase rotation tactic changes the sequence of the phase in such a way as to make the through-phase lead and the left-turn phase lagged. The effect of phase rotation is ineffective where bus volume is high [9].

*Phase Insertion* is another tactic used to provide green time for transit vehicles. This tactic strategy is applied mostly when there are several turning movement phases, and the logic is not flexible enough to handle such a case when the transit vehicle arrives in the middle of a red light, making the logic unable to apply other TSP techniques like Green Extension or Early Green. Instead, it creates a temporary green phase within a cycle. Sometimes it is called Double Realization because the transit-phase receives green time twice in one cycle. Double realization is used for a left-turn phase at an intersection with high bus requests [9]. The phase sequence used was leading left - through movement - lagging left (for the second time), which all were applied in one cycle, at a signalized intersection near a major bus terminal [9].

*Queue Jump* is another transit preferential treatment that stretches a short buslane at traffic signals, together with a specific queue jumper leading phase interval. This allows busses to receive green light sooner in order to be ahead of the queues backed-up in the adjacent lanes [11]. Queue jump was applied in a few studies and the results have shown that the combination of queue jump treatment and signal priority tactics have yielded the highest benefit in terms of transit travel time, speed, and delay as compared to scenarios in which each one is deployed separately [12, 13]. Cesme and Altun [14] studied the effect of queue jump lane on a hypothetical intersection. The results revealed that a queue jump lane corresponding to the 95th percentile queue has reduced the transit delay 1.3 times more than that of queues measured by the 35th percentile.

There are other transit signal tactics that have been introduced, which in a sense is the combination of the above listed tactics; some of which include: transit phase truncation and queue dissipation [15], early red, flush-and-return [16], expedited return [17, 18], etc.
