“Urban and suburban service” means a service performed in urban or suburban areas, or between municipalities in close proximity, except that:
(a) The one-way route mileage of the service shall not be more than 50 miles.
(b) Designated motor coach routes over state highways outside limits of incorporated cities where the one-way route mileage is over 25 miles, but does not exceed 50 miles, shall be approved by the Department of Transportation.