Except road funding, huge chunks of which come from the federal government (because, big surprise, cities and states can't afford thousands of miles of stroads and highways without invoking a government that can print its own reserve currency).
The road standards do actually allow for quite a bit of freedom. Its harder if the state DoT (Department of Highway building) is not on board. But fundamentally nothing stops engineers from doing better work. Its a matter of education and political cover.
Political will alone goes a long way, engineers are capable of self educating quite well.
A simple example is the town in Indiana that has lots of roundabouts. They are operating under the same standards but is much better in lots of way.
Engineers can do a lot by themselves and with local political cover they can do much more. If the state DoT is onboard, there is a lot of freedom.
