Unless otherwise specified in this part, the definitions in 23 U.S.C. 101(a) are applicable to this part. As used in this part:

Enforcing or Enforcement means all actions by the State to obtain compliance with size and weight requirements by all vehicles operating on the Interstate System and those roads which, prior to October 1, 1991, were designated as part of the Federal-aid Primary, Federal-aid Secondary, or Federal-aid Urban Systems.

Urbanized area means an area with a population of 50,000 or more.