THE MBTA HAS outgrown its decades-old bus maintenance garages, and T officials are considering adding around 500 buses to the fleet of roughly 1,000, which some think sets up an opportunity to make a dramatic switch towards using electric motors to haul passengers around.

The MBTA has taken some important steps in that direction, but not enough to satisfy environmentalists who want to reduce greenhouse gas emissions and harmful pollutants from diesel buses that can impact the health of Bay Staters.

The T has begun experimenting with battery electric buses, taking delivery of five articulated zero-emission buses last week. In the future, the T will purchase a mix of hybrid and battery-powered buses, and the agency wants to scrap the trackless trolleys around Harvard Square that draw electricity from catenary wires in favor of battery electric buses, said Erik Stoothoff, the T’s chief engineer.

“We have diesel-fueled buses today that our infrastructure is going to have to support, but we want to accommodate a modernized fleet that will probably be powered by electricity,” said Stoothoff. “While it would be great to go in and put the technology first, as an operating entity, we need to put the service first.”

At an event put on by A Better City on Wednesday, Stoothoff and William Wolfgang, the T’s director of vehicle engineering, were surrounded by experts and advocates focused on moving metro Boston’s transit system towards an electric bus fleet.

Black, Latino and Asian-American populations bear the brunt of transportation emissions more than white people, and tailpipe emissions contribute to asthma and other ailments in addition to speeding global warming, said Veena Dharmaraj, of Sierra Club Massachusetts.

“We need to act boldly to curb emissions particularly from the transportation sector,” Dharmaraj said.

The T officials seemed relieved when audience member Fred Salvucci, who was Michael Dukakis’s transportation secretary, argued the most immediate concerns should be getting people out of cars and onto buses – whether those buses are powered by diesel or not.

“I don’t think we should be trying to stampede the T into rushing this thing and making a bunch of mistakes. I think we should urge the T to focus on providing a lot more bus service with some judicious experimentation, which is what it sounds like they’re trying to do,” said Salvucci. “But not go gamble 100 buses on a technology that isn’t really there yet.”

Worldwide, China has taken a significant lead in the development of electric buses, according to Camron Gorguinpour, senior global manager for electric vehicles for World Resources Institute, who advised that real estate, procurement, and technical issues can create barriers for transit systems adopting e-buses, but those issues can be successfully managed.

In a report issued Wednesday, A Better City, the Boston-based business-backed group, suggested that switching to electric buses could mitigate a few problems with the T’s current bus maintenance facilities – namely the sounds and smells that emanate from them – but building electric facilities would be more costly.

Unlike diesel buses, electric buses are quiet and don’t emit noxious fumes, so electric vehicle maintenance garages could be an attractive component of a real estate project, according to the report. The report envisions converting the T’s Albany Street garage in Boston’s South End into an electric bus garage with indoor storage, charging, and maintenance facilities below a 17-story residential tower with a nearby bus transit hub.

While they are less noisy and smelly than diesel buses, e-buses take hours to be recharged, and would likely require indoor storage for best performance in the winter, according to A Better City, which acknowledges the electric bus facilities would be at least about 30 percent more expensive to build.

The MBTA has estimated that replacing all those bus maintenance facilities would cost about $875 million, according to Glen Berkowitz, project manager for A Better City. But Berkowitz said the T has only put $100 million toward that in its capital plan, and he estimates that with the need for electrification and indoor storage, the costs is actually about $1 billion or more.

It was clear from the T officials’ presentation that something will need to be done. Each of the MBTA’s 10 bus maintenance facilities is at or over capacity, the average age is 54 years old, and “many of them are functionally obsolete,” said Stoothoff.

Albany Street, which was built in 1941, is at more than three times its maintenance capacity, and two of the T garages cannot accommodate newer buses because the facilities are not tall enough, according to Stoothoff.

The only bus maintenance facility that is under capacity is the North Cambridge garage that handles the needs of the 28 trackless trolleys. Stoothoff said that, in the “short term,” the T hopes to convert that facility into one that can handle battery electric buses, which would obviate the need for expensive catenary wires along bus routes coming out of Harvard Square.

“Electric or otherwise, the maintenance facilities need investment, and we’re planning on what that investment is going to look like that can support the fleet we have today, and the evolution of that fleet from a diesel to a hybrid to a battery electric,” Stoothoff said.

A new crop of 194 hybrid buses that are going into service in the next year and a half will replace 193 diesel buses dating back to 2003-2004, according to Wolfgang. He said hybrids are more expensive to purchase than diesel vehicles, and battery electric buses are more expensive to buy than hybrids.

When it comes to maintenance, the upkeep of the electric motors is generally less costly than keeping diesel engines in repair, according to Gorguinpour.

While the T considers how large to grow its fleet of 1,017 buses, how to construct maintenance facilities that meet their needs, and how aggressively to move towards electrification, the way bus service is delivered on city streets is also undergoing some modifications. Boston, Everett and some other MBTA cities have begun using dedicated travel lanes so that buses can avoid traffic caused by personal vehicles, delivery trucks, taxis, and ride-hailing vehicles.