http://webpub4qa.wsdot.wa.gov/data/tools/bridgeclearance/is a vertical clearance planner for Washington state routes. It's under development, and has the disclaimer that it does not cover local roads, or even roads under state routes (e.g. under freeway).
The Skagit River bridge collapse a couple of years ago highlighted the need for comprehensive and accurate clearance data.
I wonder when/if the Truckers Atlas will update the clearances for that bridge. After replacing the downed span, the state replaced the curved stringers on the remaining spans.
