One Light, Two Light, Red Light, Green Light: An Analysis of Metro G Line Signal Priority (brief)

Abstract

Los Angeles County Metropolitan Transportation Authority (LA Metro) planning staff, working alongside engineers from the Los Angeles Department of Transportation (LADOT) seek to make improvements to the Metro G Line (Orange) busway to address a number of operational problems with the popular line. Since the G line busway runs on its own dedicated route, it has a significant advantage as it does not get stuck in traffic with automobiles. Speeding up the G line with current infrastructure is possible by improving transit signal priority (TSP). TSP extends green time at signals so that priority vehicles (in this case buses) can pass through an intersection without stopping. Los Angeles’s TSP system relies on the Automated Traffic Surveillance and Control System (ATSAC), a sophisticated traffic control computer housed underneath City Hall. The system, based around inductive loops buried in the pavement and embedded along light-rail tracks, decides when to grant priority to buses along the G line alignment. LADOT has certain assumptions about how G line buses progress along the alignment that reflect aspirations from when the line was built, that may not be applicable today. Additionally, dwell time is not clearly laid out in the timing charts received from LADOT. ATSAC currently relies on a transponder-based system that detects when particular buses, assigned to certain routes, fall behind on their scheduled runs.

About the Project

Buses get stuck in traffic. Allowing priority at stoplights is one possible solution to speed them along. Transit signal priority in the City of Los Angeles faces a host of constraints. These are both technology and policy based, with the City Department of Transportation relying on transponder technology that must be keyed to individual buses and hesitant to introduce additional delays for private vehicles. LA Metro would like to pilot a program to loosen the schedule- and traffic signal cycle-based restrictions put in place by LADOT. The pilot, scheduled to occur along the A (Blue), E (Expo), G (Orange) light rail and BRT lines and 720 Wilshire and 754 Vermont bus lines, could speed many more riders along some of the busiest transit corridors in Los Angeles. By introducing smoother flows for transit vehicles in Los Angeles, it may spur transit adoption by offering more competitive travel times.