if you send them by truck you’re only paying for the road maintenance

But you’re not even paying that. You’re only directly paying the vehicle tax on the truck, its fuel and amortized operation and maintenance costs. But the vehicle tax doesn’t even come close to covering the cost of the damage the truck causes to the road infrastructure. You pay the difference indirectly in other taxation that is a subsidy to the trucking industry, and also taxation that subsidizes the fossil-fuel industry.

So the bias against rail transport is even greater than you indicate.