New York City plans to convert its public bus system to an all-electric fleet by 2040, a new target announced this week by NYC Transit President Andy Byford.

“It does depend on the maturity of the technology—both the bus technology and the charging technology—but we are deadly serious about moving to an all-electric fleet,” Byford, who became head of NYC Transit in January, said at a Metropolitan Transit Authority board meeting on Wednesday.

Byford’s comments follow an ambitious action plan released on Monday that seeks to address flagging ridership and sluggish service on the nation’s largest municipal bus network. The average speed of an MTA bus in Manhattan is among the slowest of large metropolitan systems at 5.7 miles per hour. That means pollution from idling engines is much higher per mile than if the buses were going faster.

The plans calls for a “transition to a zero-emissions fleet to improve air quality and reduce greenhouse gas emissions.”

Environmental and community advocates applauded the plan.

“It’s a surprising development and a big deal big because this is the largest transit fleet in the country, with over 5,000 buses—that is the equivalent to over 100,000 electric cars,“ Kenny Bruno, a clean energy consultant, said. “It’s a big deal on climate change and public health. All New Yorkers will benefit, not just drivers and passengers but everyone who lives along bus routes and depots, a lot of whom have high asthma rates.”

A report released earlier this month by New York City Environmental Justice Alliance found 75 percent of bus depots in New York City are located in communities of color. It noted that fossil-fuel-powered buses emit air pollution linked to respiratory distress, asthma and hospitalization for people of all ages.

“These communities have been overburdened by noxious emissions for too long,” Eddie Bautista, executive director of the New York City Environmental Justice Alliance, said in a statement. The announcement by the MTA “signals to us that the Authority has heard our call for a clean bus fleet. We are pleased to receive MTA’s commitment to zero emissions and applaud their efforts.”

A study in 2016 by a researcher at Columbia University found that if New York shifted from diesel to electric buses, it could reduce health costs from respiratory and other illnesses by roughly $150,000 per bus. The study also showed that fuel and maintenance costs would drop by $39,000 per year by shifting to electric vehicles, and the city could cut carbon dioxide emissions across the fleet by 575,000 metric tons per year.

The MTA, which has more than 5,700 buses in its fleet, already is testing 10 all-electric buses and has plans to purchase 60 more by 2019. With these purchases representing only 1 percent of the entire fleet, the agency would have to significantly increase its electric bus purchases to meet its 2040 target.

Los Angeles is also shifting to electric buses. The city’s public transportation agency agreed last year to spend $138 million to purchase 95 electric buses, taking it closer to its goal of having a zero-emissions fleet, comprising some 2,300 buses, by 2030.

Details about the planned conversion to electric vehicles and how the New York agency will pay for the new buses and charging stations were not included in this week’s report. The MTA will release a full modernization plan for New York City transit in May, Byford said.