The current fleet of trolley buses is nearing the end of its life. By 2024, they will be replaced by battery electric buses.
Trolley buses have to run close to their power lines. If they catch up with each other — the chronic problem of bus bunching — they can’t pass each other. The lack of ability to pass also makes it hard to design express service. Nor can they deviate around a traffic accident. If there is a construction project in the roadway, they have to be replaced with diesel buses. And, of course, they cannot be shared with any other route that doesn’t have the necessary wires, reducing operational flexibility.
With battery electric buses, we will have the best of both worlds — a low pollution vehicle that has the flexibility necessary to provide more reliable service. And the catenary polls and wires will no longer add to the clutter of our streetscape.
That’s the positive end state that we can look forward to. Getting there, while accommodating planned road projects, is going to force the MBTA to use diesel-hybrid buses on the 71 and 73 during a two-year interim period starting this spring.
For many months, the MBTA has been working with the City of Cambridge and the Town of Watertown to develop a plan to accommodate the following major road reconstruction projects: Mount Auburn Street in Watertown, Belmont Street in Cambridge between Mount Auburn Street and the Belmont line, and Huron Avenue in Cambridge between Fresh Pond Parkway and Cushing Street. Additionally, there are two major utility installations that need to occur on Mount Auburn Street before it is paved — gas lines for the whole length and 1000 feet of 20-inch water main.
These projects would together force the de-energization of the catenary wires for over five years, forcing five years of diesel operation on the 71 and 73. However, the MBTA is going to accelerate its planned replacement of the trolleys with electric buses so that the diesel interim will only be two years.
During the two year interim, the MBTA will install the charging infrastructure needed to support a battery electric fleet out of the North Cambridge garage that currently houses the trolleys.
Replacing the trolley fleet working out of the small North Cambridge garage is a good way to test out the new battery technology at a modest scale. The diesel fleet operates out of much larger garages which are harder to convert. It will take some experimentation to work out charging and operational protocols for the battery buses. The main challenges relate to the performance of batteries in our cold weather climate.
To protect against cold weather failures, the battery buses that the MBTA plans to purchase will have a backup heater that uses diesel fuel to reduce battery drain on the coldest days. With this very limited use of diesel, the new battery fleet will be cleaner than the current mixed trolley and diesel fleet — diesel buses are routinely used as replacements for the trolleys for operational reasons.
Ultimately, the MBTA is committed to the full electrification of its fleet. As larger electrification plans have firmed up, advocates have become more comfortable with North Cambridge as an early step.
The MBTA engineers have developed a complex plan to deal with a complex set of challenges. I appreciate their efforts and I fully support their plan, even though it will mean two years of diesel operation on the 71 and the 73.
- Joint press release on the plan for the trolley buses
- Recording of February 15 public meeting about the plan
- MBTA electrification plans
- MBTA funding presentation including the North Cambridge Garage and other electrification projects
- Discussion of electrification funding on January 26 (view video at 1:13:00).
- MBTA lifecycle cost comparison for BEBs and ETBs
- MBTA carbon impact comparison of BEBs with auxiliary diesel heaters and ETBs with substitutions