Historic Cars in Maryland

I found out today that a car only needs to be 20 years or older to be considered an antique or "historic" car in the state of Maryland. This means that, according to MVA regulations the requirement for an inspection is waived and the registration for plates is around half that of other, younger cars on the road. 

There is a catch though.  Historic cars cannot be driven full-time. There is a mileage limitation. There are also restrictions on "where" you are allowed to drive. The gist of the latter is that they really don't want you driving on the highways, however, being that there are some places that can't be reached except by highway, they can't completely restrict you from getting on the highway.  Therefore, the rule for the most part reads that you "shouldn't" use the highway.