I wrote recently about the prospect of rising congestion across the region. While, in the long term, we need to think big, in the short and medium term, we have to focus on improving the operation of the transportation assets we already have — especially improving reliability and reducing delays and crowding on our bus and rail routes.
One helpful technology that is finally ready for prime time is “transit signal priority”. If we can give buses and surface light rail (the Green Line) a green light more reliably as they approach intersections, we can save precious seconds — seconds which add up to real improvements if we can control all the intersections along the route.
The MBTA has working for several years on debugging the technology. The first challenge was to get global positioning systems working in the moving vehicles so that they can report their position back to central MBTA systems in real time. GPS is operational now in most of the MBTA’s bus and light rail fleet. The consolidated GPS data feed from the fleet of vehicles is what is allowing the development of “where is my bus” smartphone apps.
The second challenge is to figure out how to tell the lights to turn as the transit vehicle approaches them. This requires different solutions in different communities, depending on how their stop lights are controlled. In Boston, where the lights are connected to a central system, the request to change the light goes from the MBTA’s central system to the city’s central system, which in turn directs the lights. In other communities, a cellular transmission runs directly to a device installed in each light’s control box.
The MBTA now has transit priority working at six intersections — 4 in Boston on the Green Line (E and B branches), 1 in Brookline on the C branch of the Green Line and one on Mass Ave in Central Square Cambridge for the Dudley bus.
The next step will be to roll the technology out to four full high-ridership corridors — Beacon Street in Brookline, Commonwealth and Huntington Avenues in Boston and Massachusetts Avenue in Cambridge. All together, this will mean getting the technology in place at 89 intersections for a cost of approximately $12,640 per signal. The MBTA board recently approved this step at a recent hearing at which I testified in support.
Once the technology is in place along a full corridor, the seconds saved at each intersection will add up to reduce the probability of bunching and improve end-to-end run time. The most common complaint commuters have about bus service is bunching. Bunching arises when a lead bus is delayed by lights or traffic conditions. The delay results in more people waiting at each stop, which in turn means more delays in boarding. The delays cascade and trailing vehicles start to catch up and, on trolley lines, cannot pass.
After TSP is working on these first four very high-ridership corridors, the T will be looking for other high-ridership, high-delay routes in communities that are eager to partner and make the technology work. I’m hopeful that we can get TSP going on several routes in my district, top among them the 71 (Watertown) and 73 (Waverley) which are the two most crowded routes in the MBTA system.
Transit signal priority on the 71 and 73 will work well with the improvements currently under study in the segment of these routes in front of the Mount Auburn Cemetery, where buses often lose several minutes waiting in traffic — more on these improvements in a future post.