Transit Signal Priority System to Optimize Traffic for Bus & Rail

EMTRAC Transit Signal Priority (TSP)

The EMTRAC system utilizes precise GNSS technology and secure wireless communication to provide reliable, safe, and efficient signal priority. The EMTRAC system has led the way for over 30 years—and it continues to lead the way with intelligent signal priority.

While progressing along their routes, EMTRAC-equipped vehicles evaluate real-time conditions to determine whether signal priority is necessary in order to stay on schedule. When needed, the vehicle transmits a signal-priority request for the appropriate intersection.

Any number of factors may influence whether signal priority is granted, including time-of-day, passenger load, amount of time behind schedule, time since last granted request, and many others. EMTRAC is completely automatic and requires no driver interaction.

Signal Priority without Traffic Disruption

Arrival times vary according to traffic conditions and are reported by EMTRAC-equipped buses.

Adaptive Priority

Adaptive priority is a strategy for adjusting signal control based on real-time traffic conditions. “Its application to TSP continuously optimizes the effective timing plan based on real-time, observed data, including transit vehicle location.”[1]

The EMTRAC system provides the data needed to implement, or improve, adaptive systems by notifying the signal controller when an approaching bus reaches pre-defined ETA timepoints during its approach (for example, when it is 90, 60, 35, and 15 seconds from the intersection).

This system is unique to North America and takes advantage of features built into many signal controllers and TSP firmware. It reacts to changes in on-street congestion and bus-approach speeds in real time. As traffic volumes fluctuate, so do the positions of ETA time-points.

Upon receiving the bus ETA notifications, the traffic controller preconditions its internal timings in preparation of its arrival at the intersection. The advanced time-points help the signal controller gradually modify the timings to reduce the impact on the intersection while also maintaining coordination with other intersections along the corridor.

_{Applicable Patent: US No. 8,878,695}

EMTRAC-Equipped BRT, Brampton, ON (photo by Sean Marshall)

Conditional Priority

Conditional priority utilizes real-time vehicle status to determine whether signal priority should be requested—and it is often the best solution for achieving effective transit performance with minimal traffic disruption.

According to ITS America, “Conditional priority means that a smaller percentage of transit vehicles are requesting priority, but may be viewed as preferable if the emphasis is more on improving service reliability than on decreasing absolute travel time.”[1]

In addition to many other possible conditions, TSP may be based on the following:

Time Behind Schedule
Time Since Last TSP Request
Door Status (open or closed)
Stop-Request Status
Passenger Load (Total or Percentage)

How Will Conditional Priority Work for You?

The EMTRAC system is capable of handling conditional factors in a number of methods—depending on your available capabilities. These methods include:

Connection to Onboard Transit Computer: The transit computer outputs conditional status to the EMTRAC Vehicle Computer Unit (VCU). For example, the transit computer determines that the bus is five-or-more minutes behind schedule and outputs this status to the EMTRAC VCU, which requests priority until the bus status is once again within the pre-defined time frame.
EMTRAC Priority Detector Determines Status: The intersection-based Priority Detector calculates the conditional status and responds accordingly. For example, if a bus on Route 180 has requested priority at a given intersection within the last five minutes, the Priority Detector does not forward priority requests from Route 180-buses during the pre-defined time frame.
AVL System Determines Status: EMTRAC Central Monitor (or third-party transit AVL system) determines vehicle and/or intersection states and outputs that data to the intersection-based Priority Detector, which carries out (or withholds) priority requests as a result.

For information about how the EMTRAC system is used to generate conditional priority in Brampton, Ontario, please read the Transit Applications and EMTRAC System white paper.

Actuated Left-Turns (A) and Queue-Jump Lane (B) Transit Priority

Actuated Priority

Actuated transit phases allow equipped buses to request priority for specific intersection lanes. For example, left-turn lanes are given signal priority when buses enter the pre-defined left-turn zone and request priority for that specific lane.

EMTRAC utilizes multiple global navigation systems, augmented by inertial navigation (three-axis gyro and accelerometer), to deliver precise actuated priority requests.

Actuated transit phasing may be implemented with the EMTRAC system in the following ways:

Exclusive Left Turn Lanes: Use EMTRAC software to easily define any turning lane to allow TSP without affecting other lanes and phases.
Queue Jump Lanes: Grant lead-phase priority to buses at near-side stops, bays, and lanes to allow them to re-enter mainstream lanes before general traffic.
Freeway Ramp Meters and Queue Bypasses: Enable equipped buses to reduce freeway ramp meter wait times. In areas with queue bypass lanes, request priority for the bypass lane without affecting the mainstream ramp lane.
Gate-Controlled Lanes or Garages: Request gates to open for equipped vehicles—without requesting access to nearby vehicles that are not adjacent to the gates.

TSP Features

Conditional Signal Priority enables equipped vehicles to request priority only when agency-specified conditions are met.
EMTRAC ETA technology enables traffic agencies to implement Adaptive Signal Control for intersections, including those not equipped with adaptive-capable controllers or other third-party inputs. The ETA feature updates controllers of calculated time-of-arrival based on current traffic conditions (U.S. Patent No. 8,878,695).
Systems Manager interface allows easy customization for individual vehicles, vehicle classes, or intersections. For example, rapid transit buses may request signal priority earlier than local metro buses.
Precise satellite and inertial positioning enable actuated requests by lane, even in the most difficult conditions (such as in urban canyons or under large overpasses).
Detailed logs and reports show vehicle and intersection activity by date and time. The EMTRAC system may also automatically email periodic reports to specified personnel.
Priority-request start points may be based on time-of-day to allow for earlier controller requests during peak-period rush hours.

TSP Benefits

The benefits of TSP are well documented—and EMTRAC-system features reduce traffic disruption and unsynchronized signals
Installation and maintenance time is significantly less than with any other TSP system.
Offers the most advanced TSP features without requiring the latest signal-controller equipment.
Improves schedule adherence and headway times by enabling transit vehicles to request priority only when behind schedule.
Helps reduce fuel costs by decreasing intersection delays.
Interfaces with EMTRAC Central Monitor to enable transit personnel to track vehicle progress and activity.

EMTRAC TSP

Transit Headway

References

1. Baker, Ronald J., et al. An Overview of Transit Signal Priority. Ed. James Chang. Washington, DC: Intelligent Transportation Society of America. 2004. ITS America.

Video

EMTRAC System video demonstrations of EMTRAC System capabilities, including Emergency Vehicle Preemption (EVP), Transit Signal Priority (TSP), transit rail safety, vehicle detection, and signal management.