The Connecticut Department of Transportation is seeking permission to resume buying diesel buses after a two year hiatus due to a national backlog in the manufacturing of newer battery-powered buses.

The agency has been prohibited from adding new diesel buses to its transit fleet since Jan. 1, 2024, as of a part of a wider effort to convert the state-owned fleet to electric. Earlier this week, however, DOT officials told lawmakers that the ban has made it difficult for the agency to keep enough buses in service for riders across the state.

The agency has proposed legislation, House Bill 5464, that would lift the ban while maintaining a separate requirement to transition at least 30% of its transit fleet to zero-emission vehicles by 2030.

“Without the flexibility to purchase some additional diesel buses while the electric bus industry and infrastructure continue to develop, ConnDOT will not be able to replace aging vehicles quickly enough to maintain our current service levels,” Deputy Commissioner Laoise King said Monday.

King said the agency is confident it will be able to meet the 30% zero-emissions target and it continues to support a broader effort to lower greenhouse gas emissions from the transportation sector. However, she said the limited number of U.S. manufacturers has resulted in waits of up to two years for new electric buses.

Connecticut has a fleet of more than 600 transit buses, including 61 fully electric buses and 77 hybrids. King said the current law, as written, prevents the agency from buying additional hybrids that run partially on diesel.

DOT Commissioner Garrett Eucalitto also provided written testimony to lawmakers, in which he explained that the state’s electric bus fleet has been affected by battery recalls that limit their performance. In order to purchase costlier electric buses, he wrote, the state had relied on federal funding that is now in doubt due to shifting priorities under the Trump administration.

It was not the first time state officials have faced difficulty meeting vehicle electrification deadlines set by lawmakers. The same law that enacted the ban on new diesel buses, the Connecticut Clean Air Act of 2022, set a goal of electrifying half the state’s fleet of smaller cars and trucks by Jan. 1, 2026. Last year, the Department of Administrative Services, which oversees the state fleet, admitted it was nowhere near reaching that goal. And just after the deadline passed earlier this year, DAS released a report showing it fell far short its goal.

Lori Brown, the executive director of the Connecticut League of Conservation Voters, called diesel engines “the absolute worst” in terms of sooty pollution and said that lawmakers and the DOT should explore other alternatives before lifting the ban.

“Anybody who’s ever stood on a corner and watched a bus go by and just get blasted by diesel would know why we wanted to get rid of that,” Brown said.

The DOT bill is currently pending before the legislature’s Transportation Committee, which has yet to schedule a vote on the topic.

Another piece of legislation before the committee, Senate Bill 416, would roll back existing requirements for the electrification of school buses after officials in several districts raised concerns about the costs. Those requirements were also put in place as a result of the 2022 Clean Air Act.

Instead of being required to convert 100% of their school bus fleet to zero-emission vehicles by 2040, districts would only have to switch over 90% of vehicles and would have an additional six months to do so.

The bill would also sharply reduce earlier deadlines for districts located within environmental justice communities to switch over to electric and zero-emission vehicles. Instead, districts in distressed municipalities would only have to meet a 10% zero-emissions target starting in 2030, which would gradually increase over the next decade.

Last month, school officials in Branford announced plans to launch the state’s first all-electric bus fleet starting in the next school year.

But Jean Cronin, executive director of the Connecticut School Transportation Association, told lawmakers on Monday that no other school districts in Connecticut were likely to meet the mandates. The cost of battery-electric buses, in addition to the necessary charging infrastructure, can be up to four times that of diesel powered buses, she said.

Those costs are particularly burdensome on large school districts located in lower-income cities and towns that are currently subject to the earliest deadlines, Cronin said. Some districts have explored alternatives involving cheaper and cleaner-burning fuels such as propane, she added.

“These are the municipalities that have the largest number of school buses, and their school budgets are the most constrained, so they have the least amount of resources to be able to purchase these vehicles,” Cronin said.