In the US at least the state DOT's have that information and have a GIS office that would make it available for a nominal fee. You'd still need to check a lot i

In the US at least the state DOT's have that information and have a GIS office that would make it available for a nominal fee. You'd still need to check a lot it in cities. Big worry would probably be liability; if your database of overpasses has an error (inevitable) can the truckers insurance company hold you financially responsible for relying on your app?