Pittsburgh Regional Transit, the region’s largest transit authority, announced it will be ramping up its purchasing of electric buses by 2025 and is committing to buying zero-emission buses exclusively come 2032. It’s a move that will tentatively see PRT reach its newly-set goal of having a fully zero-emission fleet by 2045.

It will cost PRT an estimated $1 billion to fulfill such an endeavor over the next 20 years of the transition, though that’s not a new expense in its entirety.

According to PRT CEO Katharine Kelleman, the transit authority’s buses tend to have a lifespan of 12 years and as old buses are phased out, new ones are regularly bought to replace them. PRT said a 40-foot electric bus costs about $1 million to purchase, about 60% more than its roughly $600,000-$700,000 diesel-powered equivalent. However, Kelleman said that over the lifetime of both buses, the roughly 20 parts found in the electric engine are cheaper and easier to replace compared to the more than 300 parts that make up its diesel-burning alternative.