By Logan Dredske
Fixed-route buses are the most common form of public transit in the United States; however, bus ridership has been falling in recent years after enjoying a surge in the early- to mid-2000s. Efficiency in all aspects of the transit network is important if transportation agencies want to encourage increased transit use. New York City is trying to improve the efficiency of its bus service by implementing transit signal priority (TSP.)
Although New York City is home to the largest transit agency and the highest number of average weekday bus riders among major cities, much work remains to lure more riders. New York bus ridership has decreased 5.6 percent from 2011 to 2016. With an average bus speed as low as 7.4 mph during weekdays, the city also has some of the slowest moving buses. And bus speeds for the city are slowing, with a 2 percent decline between 2010 and 2015. Implementation of TSP is an effort to improve average speeds.
TSP is a system that coordinates buses with traffic signals to limit the time buses are stopped at traffic lights, thereby reducing travel times for passengers. As discussed in the U.S. DOT handbook on TSP, the system reduces travel times using active and passive priority systems. A passive priority system requires understanding the transit operations (e.g., travel speeds, number of stops, dwell time at stops) to coordinate traffic signals to match travel patterns of buses. An active priority system allows the bus to directly communicate with the traffic signals to extend a green signal, shorten a red signal, or display an exclusive left turn signal for the bus at the approaching intersection. TSP systems can also be programmed to adjust traffic signals via continuously monitored traffic conditions, or by considerations of the trade-offs between transit and traffic delays.
Since 2012, NYC DOT worked with the Metropolitan Transportation Authority to implement TSP systems at 260 intersections on five bus corridors. The NYC DOT recently released a report comparing bus travel times during peak periods before and after the implementation of TSP systems. Bus travel times were reduced in every corridor and at each time period analyzed. The decreases ranged from five to 30 percent, with the average being an 18 percent reduction. General traffic flow improved after implementation as well. In addition, NYC DOT indicated where TSP systems work best: two-way streets that do not have existing “green wave” signals, intersections that do not have a lot of cross traffic or many turn signals, and streets that have predictable bus travel times such as streets with bus lanes.
Other cities in the U.S. have used TSP systems in hopes of encouraging residents to utilize public transit. Travel time savings associated with TSP in North America have ranged from two to 18 percent, with average reductions of eight to 12 percent. Major cities such as Los Angeles and Chicago have seen 7.5 and 15 percent average reductions in travel times, respectively. NYC DOT and MTA’s future transit plans involve the increased utilization of TSP systems as a means of continually striving to improve bus travel times for riders.
Logan Dredske is a Project Assistant at SSTI.
By Logan Dredske