There is some guidance on that in the MUTCD...He can act as a flagger but has to signal clearly per the guidance.. "otherwise directed by officer provision" note: mutcd is adopted by CO...
http://mutcd.fhwa.dot.gov/HTM/2003r1/part6/part6e.htm
http://198.187.128.12/colorado/lpext.dll?f=templates&fn=fs-main.htm&2.0
42-4-603. Obedience to official traffic control devices.
Statute text
(1) No driver of a vehicle shall disobey the instructions of any official traffic control device including any official hand signal device placed or displayed in accordance with the provisions of this article unless otherwise directed by a police officer subject to the exceptions in this article granted the driver of an authorized emergency vehicle.
(2) No provision of this article for which official traffic control devices are required shall be enforced against an alleged violator if at the time and place of the alleged violation an official device is not in proper position and sufficiently legible to be seen by an ordinarily observant person. Whenever a particular section does not state that official traffic control devices are required, such section shall be effective even though no devices are erected or in place.
(3) Whenever official traffic control devices are placed in position approximately conforming to the requirements of this article, such devices shall be presumed to have been so placed by the official act or direction of lawful authority unless the contrary is established by competent evidence.
(4) Any official traffic control device placed pursuant to the provisions of this article and purporting to conform to the lawful requirements pertaining to such devices shall be presumed to comply with the requirements of this article unless the contrary is established by competent evidence.
(5) Any person who violates any provision of this section commits a class A traffic infraction.
History
Source: L. 94: Entire title amended with relocations, p. 2340, § 1, effective January 1, 1995.
