Approach or exit road shall mean any highway or ramp designed and used solely for the purpose of providing ingress or egress to or from an interchange or rest area of a highway. An approach road shall begin at the point where it intersects with any highway not a part of the highway for which such approach road provides access and shall terminate at the point where it merges with an acceleration lane of a highway. An exit road shall begin at the point where it intersects with a deceleration lane of a highway and shall terminate at the point where it intersects any highway not a part of a highway from which the exit road provides egress.