In accordance with Transportation Code, Chapter 623, Subchapter G, the department may issue a permit for the operation of an oil well clean-out, drilling, servicing, or swabbing unit, which is a piece of fixed-load mobile machinery or equipment used for the purpose of cleaning out, drilling, servicing or swabbing oil wells, when the unit cannot comply with one or more of the restrictions set out in Transportation Code, §621.101. The sections in this subchapter set forth the requirements and procedures applicable to those permits.