Highlight a Road Map Mashup
http://www.territoryguide.com/roads.htm
This mashup allows selecting a road by clicking on it. Most interstates, state highways and US highways are included and a lot of numbered roads as well. Some local roads show. The highlighted portion (an encoded GPolyline object) will be limited to one state.
The database is proprietary but NOT part of Google's (or anyone else's) directions or route finding service. It's 100% self contains on our servers. The database is available for license, interested parties please contact us directly for terms and costs. There is no web service available to pull road data from our database.