Greenwashing the MBTA’s hybrid buses
New vehicles will shift pollution burden to Chelsea, East Boston
“At Silver Line Way, you will hear the bus’s engine shut down for just a moment, as it converts to diesel power for the rest of the trip to Logan Airport.”
These words have been repeated on every Silver Line trip since 2004, as buses have transported millions of passengers between South Station, Logan Airport, and, more recently, Chelsea. The builder of these buses, Neoplan, went out of business shortly after the buses were delivered, and the buses are beyond their useful lifespan. The MBTA’s Fiscal and Management Control Board plans to vote next week on a proposal to replace these “dual-mode” diesel-electric buses with something cryptically referred to as “enhanced, electric hybrid” buses, often referred to as EEH buses.
This EEH moniker is a particularly insidious example of “greenwashing.” The proposed model is a New Flyer XDE60 model. “X” refers to the model (Xcelsior) and “60” refers to the length of the bus. “DE” describes the drivetrain: diesel-electric hybrid. EEH conveniently leaves out the fossil-fuel origin of all of the power for the bus. In fact, except for some compressed natural gas buses, all but the oldest members of the MBTA’s bus fleet are “hybrid” buses.
Hybrids use a diesel generator to charge a battery and operate an electric drivetrain from the battery, allowing the diesel engine to operate more evenly and to shut down when the bus is stopped or coasting and the batteries are already charged. Such hybrid buses are more expensive to buy than straight-diesel buses, but quieter, cleaner, and cheaper to operate.
Despite nearly double the cost, the other “enhancement” of an EEH bus is simply a larger battery, allowing the bus to operate for a longer distance in “all-electric” mode. Yet all of the power used to move the bus will still be generated by an on-board diesel generator, and any reduction in fuel use and emissions will be minimal compared with an existing hybrid. The extended all-electric mode will be used in the Silver Line tunnel, which does not have the ventilation needed to run diesel buses. While the current fleet is powered, in part, by overhead electric wires, the new fleet will be run entirely by diesel engines. This means that, to charge the batteries, the buses will have to run the diesel engine outside of the tunnel, not just to provide propulsion for the bus, but also to charge the batteries for the in-tunnel travel.
Charging the batteries while providing propulsion will lead to higher transit emissions in these areas than a non-enhanced hybrid bus. There will be no change to emissions in the Silver Line tunnel itself, but there will be increased emissions in East Boston and Chelsea, areas which already have some of the worst air pollution—and COVID-19 vulnerability—in the region. Averaged across the three Silver Line routes which use the Seaport tunnel, generating power for use in the tunnel will increase the use of the diesel engines elsewhere by approximately 65 percent. This shifts pollution from the Seaport, one of the whitest communities in the region, to East Boston and Chelsea, where most residents are people of color. It is analogous to siting a new, fossil fuel power plant in Chelsea to serve the electricity needs in the Seaport.
This is hardly an equitable, or acceptable, solution. The burden of pollution for these transit vehicles will fall upon some of the most disadvantaged areas in the Commonwealth. While the proposed EEH buses may be cleaner than the current 2004-era diesel buses (now the oldest buses in the MBTA fleet), there are far better alternatives, ones which can use the existing electrification infrastructure in South Boston to provide zero-emissions transit in East Boston and Chelsea.
Rather than burdening East Boston and Chelsea with generating power for service in the Seaport, buses with batteries on-board could charge off the overhead wire in the Seaport Tunnel and then operate the rest of the route emission-free. (The “burden” of power generation will fall on the MBTA’s engineering and infrastructure department to maintain overhead wire, which it has done since the first horsecars were electrified 132 years ago.) This power is generated off-site, and as the regional power system uses more wind, solar, hydro, and other zero-emissions power, these buses will become even greener. With the wires already in place, there will be no need for the T to invest millions of dollars in new charging infrastructure. Most importantly, it will not saddle East Boston and Chelsea with increased emissions.
These buses are already widely available. Dayton, Ohio, which has an extensive trolleybus network and an aging fleet, faced a similar decision in 2013. It tested two versions of a “next-generation” trolleybus. One, like the MBTA’s current Silver Line fleet, had a diesel engine for off-wire travel. The other had a battery. After three years of extensive testing, the agency chose the battery version for its next-generation trolleybus fleet. The bus charges while operating under the wires, and has a range of 15 miles on battery power off-wire. (This battery is just 10 percent the size of a fully battery-electric bus.)
This is nearly twice the off-wire distance of the longest Silver Line Route—the SL3 to Chelsea—meaning that a fleet of these “in-motion charging” buses could serve the SL1, SL2, SL3 and eventual extensions, using the existing overhead wire to charge. Rather than increasing emissions from these buses in Chelsea and East Boston, it would reduce them—to zero. These buses cost Dayton $1.2 million each for 40-foot buses; 60-foot buses are typically 50 percent more expensive. This would put the cost of a battery-trolleybus hybrid fleet, adjusted to 2020 costs, at $87 million, allowing the T to run zero-emission buses for less than the cost of the EEH fleet.The MBTA’s engineering department appears not to have considered this option. It should. Instead, it denigrates overhead wire as “burdensome” to maintain and operate. Most of its complaints regard issues operating buses when there are problems with the power system, yet this is easily solved since every trolleybus used today has off-wire capability. Larger trolleybus fleets in San Francisco, Seattle, and Vancouver have smaller batteries than the Dayton fleet, but can still operate several miles off of the overhead wire.
Ari Ofsevit is Boston program senior associate at the Institute for Transportation and Development Policy and a board member of TransitMatters.