It varies by state, the best thing to do is check with a steel fabricator. They have people who deal with shipping. Generally something under 14' high should be OK on the interstate, but sometimes there are spots with substandard clearances.
FYI - In NY, it's possible to get tub girders up to 145' to locations north of NYC. Within the city, stringers/girders up to 100-125 feet are possible, as long as the weight is generally under 100T.
