The American Independent Truckers' Association maintains a website that has clearance data available in the public section.
www.aitaonline.com Select "Information" from the top menu bar, then you can select each state and see road, bridge height, and clearance data listed by road within the state.
I've used this for a few years, haven't been misled yet.
John & Diane, fulltiming since '12
'02 DS, FL, Cat, '04 Element
NHSO RVM103