Colorado Law for Residents (C.R.S. 42-4-214)
"Whenever an authorized service vehicle is performing its service function and is displaying lights as authorized in subsection (1) of this section, drivers of all other vehicles shall exercise more than ordinary care and caution in approaching, overtaking, or passing such service vehicle and, in the case of highway and traffic maintenance equipment engaged in work upon the highway, shall comply with the instructions of section 42-4-712"
"Any person who violates any provision of this section commits a class B traffic infraction; except that a person commits a class A traffic infraction if the person passes an authorized service vehicle snowplow that is operated by a state, county, or local government, displaying lights as authorized in subsection (1) of this section, and performing its service function in echelon formation with one or more other such snowplows."