Then you cut spending on less crucial projects to pay for it.
At least, that's what you do if you aren't a leftist.
I actually disagree. Here in my state, we vote on property tax levys for school funding all the time. If we passed no levys, there would be no funding for public schools, fire departments etc ...
Here’s the way that folks in Massachussetts get their road funding (like, say, the Big Dig project in Boston). Earmark some pork spending and hide it in a 3000 page omnibus spending bill.