It seems like the point isn't that it's intended to tax EVs, it's intended to shift the cost of road maintenance onto the vehicles that cause most of the road maintenance needs. Basically, it's aligning incentives so that firms bear the true cost of their actions.

If that results in taxing semi and heavy duty trucks, that may be a good thing. A lot of the wear & tear on highways comes from trucking; if it shifts a lot of that truck traffic to rail, it likely would significantly reduce the total cost to society.