Mo. Rev. Stat. § 304.580
As used in sections 304.582 and 304.585, the term "construction zone" or "work zone" means any area upon or around any highway as defined in section 302.010 which is visibly marked by the department of transportation or a contractor or subcontractor performing work for the department of transportation as an area where construction, maintenance, incident removal, or other work is temporarily occurring. The term "work zone" or "construction zone" also includes the lanes of highway leading up to the area upon which an activity described in this subsection is being performed, beginning at the point where appropriate signs or traffic control devices are posted or placed. The terms "worker" or "highway worker" as used in sections 304.582 and 304.585 shall mean any person who is working in a construction zone or work zone on a state highway or the right-of-way of a state highway, any employee of the department of transportation who is performing duties under the department's motorist assist program on a state highway or the right-of-way of a state highway, or any utility worker performing utility work on a state highway or the right-of-way of a state highway. "Utility worker" means any employee or person employed under contract of a utility that provides gas, heat, electricity, water, steam, telecommunications or cable services, or sewer services, whether privately, municipally, or cooperatively owned, while in performance of his or her job duties.
§ 304.580, RSMo