This is generally a bad thing, but very concretely it led to road traffic growing much faster than rail traffic (or canal ship traffic) even in countries with a very dense rail network.
Comparing this with free public education, by not charging user fees to attend school, we are subsidizing (a) having children, and (b) educating them at the expense of the childless and I guess people who don’t want to educate their kids. We subsidize those because we believe they are truly public goods that are better for everyone in the long run. Encouraging people to drive more and ship more things by truck is not necessarily better for everyone.
Hence greatly increasing chances of finding better or any employment and at least partially reducing pressure employers can come up with.
...
You load sixteen tons, what do you get?
Another day older and deeper in debt
Saint Peter don't you call me 'cause I can't go
I owe my soul to the company store
...To each their own.
That said, you should listen to the podcast “Nice White Parents.” It points out that this model of underfunding the schools and making up for it with donations is essentially letting wealthy families buy their way out of the problem while leaving disadvantaged students behind.
I can't help but see this as a regressive use tax in many ways, since it'll likely apply to lower value items at a higher proportion which is what poorer people would be buying. The end user pays in either case, but doing it through taxation policy allows for a measured approach.
Here in Sydney we just opened a tolled tunnel, and to ease congestion up above on the older commuter road all trucks must use this tunnel. I don't know all the factors but it sounds like the best option for the people, they have a choice and trucks pay their way.