If trucks paid their way, more goods would travel by freight rail.
Beyond that, have you ever bothered to notice those little areas on the side of highways called weigh stations? You know, the ones where you don't have to stop? Yeah.
If anything, the subsidy runs from truckers to casual drivers, not the other way around.
The point is that heavy trucks don't pay enough taxes to cover their actual impact on the road-system.
The reason it doesn't happen is because then you've got to pay additional drivers, which outweighs the cost savings from avoiding the additional road use taxes.
I feel the need to add the qualifier that this is true of federal roads, but less so as we talk about local roads. I realize the story pertains to the interstate system, but as a cyclist the widespread misconception that gas tax funds all roads and other users are somehow freeloaders is quite detrimental.