What's the best map to use for routing?

An atlas is not defined enough to show all roads but it will give you lots of info on low under passes and not always accurate . I keep state maps (pick up at rest areas) they are quite helpful for those smaller roads. Some states will have most of the info your looking for on line at their web site , hope your not in a hurry- takes time to dig deep in some of them. Link after link after link after link.

 

Sometimes you can find little maps more for the state, a lot of rest areas used to keep them or smaller gas station types, NC is weird though

 

I run into this occasionally. PA is great for putting odd numbers for roads. Pretty much just do a Google search on the area then find a county map. It's not perfect and takes a little time. A good example of this is SR 0300 in PA.

 

I've also found, by varying degrees, that State and city DOT sites can be useful to find such info.
Had to route myself into Oakland California. The route I was given was wonky and would lead me to the receiver (little tiny place where you park on the road beside them and they unload you with a forklift and a guy in the trailer with a palletjack) pointed in the wrong direction. I was able to find the truck restricted roads info on the Oakland city website and it helped me find a route that actually worked.

 

When in doubt call the state permit office.
I use the road atlas and Google.

Or call the company that got you the permit
If you don't self-issue.
Good luck

 

Google maps and common sense.