Stop at any truck stop and pick-up a "Motor Carriers Atlas". I know that this is low tech, and the old stubby pencil paper way, but as a 20+ year truck driver this is an invaluable tool for not only low bridge clearances but restricted highways, i.e. in NY state all commercial vehicles are prohibited from traveling all Parkways, reason - Low Bridges!, and these low bridges might not show up on trucker type GPS's and it's too easy for an RV'er to get on one and then be in trouble.
2012 Winnebago "Journey To Insanity" 40U
2008 Dakota Sport 4x4
2004 Subaru Baja - DW's
2006 Honda Shadow Aero - TOAD for now.