DeKalb County, Georgia features an excellent example of a Bus-Rapid-Transit (BRT) line with traffic signal priority and queue jump lanes. The partnership of DeKalb County, the Metropolitan Atlanta Rapid Transit Authority (MARTA), the Georgia Department of Transportation (GDOT) and the Federal Transit Administration (FTA) has effectively implemented BRT on the major arterial of Memorial Drive.
As detailed yesterday, (BRT) is a transit line that can bypass congestion. BRT service operates in a dedicated lane or receives signal priority via queue jumpers. With the exceptions of New York City, the District of Columbia, downtown Chicago, and central San Francisco, the frequency of bus service is not high enough to dedicate an entire lane to buses. As a result dedicating an existing lane to buses is an inefficient use of the roadway. Further, it is sure to enrage automobile drivers. Since these corridors have fewer than 60 buses an hour or less than one bus a minute, the best solution for most places is offering signal priority via queue jump lanes
In priority signaling, a bus has special equipment that alerts a traffic signal that it is approaching the intersection. In some situations, the traffic signal will turn green in a matter of seconds so the bus does not have to stop for a red light. In other situations the bus gets a priority green; a priority green gives the bus a 5-20 second head start over other vehicles. BRT systems with priority signaling typically have either a dedicated lane at intersections or share traffic with the right-lane. This allows the bus to jump ahead of traffic when the light turns green.
DeKalb County deputy director of Engineering Peggy Allen detailed the Memorial Drive service in the Partnering for Improved Transit Service session at last month’s Institute of Transportation Engineers Annual Meeting and Exhibit. DeKalb County in the Atlanta region first implemented traffic signal priority in 1999 along busy Candler Rd. Traffic signal priority gives preference to local buses at 17 major intersections. Then, DeKalb County worked with MARTA, GDOT and FTA to implement the Memorial Drive Bus-Rapid-Transit service with signal priority at 27 intersections.
The Memorial Drive project is being evaluated against three main goals: improving air quality, providing cost-effective transit service and reducing traffic congestion. The DeKalb County project features signal prioritization, queue jumper lanes at intersections, electronic information displaying bus arrival times and multi-door boarding. There are two BRT services that operate along much of the 5-mile corridor during rushhour. Each operates every 10 minutes.
The BRT vehicles have special radio/GPS emitters. The emitter sends speed, heading and position information that is updated each second. The data sent by the emitter is received by the radio/GPS receiver, which is located near the signalized intersection. If the vehicle is approaching while the signal is green, the detector prompts a sequence within the controller that provides for additional green time to get the vehicle through the intersection. This allows all vehicles in parallel lanes to clear the intersection as well.
If the BRT vehicle is approaching the intersection on a red signal, the traffic signal phases for the side streets revert to minimum cycle times to allow a green signal for the approaching vehicle as soon as feasibly possible in the timing sequence. One unique aspect of the system is that it maintains signal coordination along the corridor.
Several of the intersections make use of queue jumpers. The concept allows the bus, which is in a restricted travel lane, to receive a green indication at the traffic signal while other vehicles remain at a stop condition at the same intersection, thus giving the bus priority in the queue.
In order to differentiate between the signal indications for the normal traffic signal phases and the queue jumper signal phase, the two-lens light rail transit signal indication was used as the signal indication in the BRT lane. Both the go and the stop indications are white, which prevents any possible confusion for motorist in the travel lanes parallel to the queue jumper lane. Additionally, a “Bus Signal” sign was displayed at the intersection adjacent to the light rail transit signal indication to further differentiate them from the usual signal indications.
Having the appropriate traffic signal timing plan in place is critical to ensuring the proper operation of the system. Prior to implementing the transit signal priority system the morning rush hour timing plan had a cycle length of 150 seconds and used eight phases of the controller. After implementing the system the cycle length for the corridor was increased to 160 seconds. Additionally, the queue jumper installation necessitated the addition and utilization of a ninth phase, separate from all of the other phases in the cycle.
Preliminary data show that this BRT line has decreased congestion by more effectively using the roadway and by providing a more reliable, more used bus route. At the same price as a local bus, the Memorial Drive BRT lines offer better, more reliable service at a low price. Finally, improved travel speeds for both cars and buses has reduced pollution. While ridership is very strong, the service could be improved further if queue jump lanes were built at the remaining intersections. The Memorial Drive corridor is similar to other congested arterial corridors around the nation. If the service works in DeKalb County it can work most everywhere else.