Slow Drivers, Left Lane, Slower Traffic Keep Right, Keep Right, Move Over, Driving Left Lane, Passing

(a) Upon all roadways of sufficient width a vehicle shall be driven upon the right half of the roadway, except as follows:

(1) When overtaking and passing another vehicle proceeding in the same direction under the rules governing such movement;
(2) When an obstruction exists making it necessary to drive to the left of the center of the highway; provided, any person doing so shall yield the right-of-way to all vehicles traveling in the proper direction upon the unobstructed portion of the highway within such distance as to constitute an immediate hazard;
(3) Upon a roadway divided into three marked lanes for traffic under the rules applicable thereon; or
(4) Upon a roadway restricted to one-way traffic.

(b) Upon all roadways any vehicle proceeding at less than the normal speed of traffic at the time and place and under the conditions then existing shall be driven in the right-hand lane then available for traffic, or as close as practicable to the right-hand curb or edge of the roadway, except when overtaking and passing another vehicle proceeding in the same direction or when preparing for a left turn at an intersection or Colorado Statutes 42-4-1013. Passing lane - definitions - penalty

(1) A person shall not drive a motor vehicle in the passing lane of a highway if the speed limit is sixty-five miles per hour or more unless such person is passing other motor vehicles that are in a nonpassing lane or turning left, or unless the volume of traffic does not permit the motor vehicle to safely merge into a nonpassing lane.

(2) For the purposes of this section:

(a) "Nonpassing lane" means any lane that is to the right of the passing lane if there are two or more adjacent lanes of traffic moving in the same direction in one roadway.
(b) "Passing lane" means the farthest to the left lane if there are two or more adjacent lanes of traffic moving in the same direction in one roadway; except that, if such left lane is restricted to high occupancy vehicle use or is designed for left turns only, the passing lane shall be the lane immediately to the right of such high occupancy lane or left-turn lane.

(3) A person who violates this section commits a class A traffic infraction. into a private road or driveway.
(c) Upon any roadway having four or more lanes for moving traffic and providing for two-way movement of traffic, no vehicle shall be driven to the left of the center line of the roadway, except when authorized by official traffic-control devices designating certain lanes to the left side of the center of the roadway for use by traffic not otherwise permitted to use such lanes, or except as permitted under subsection (a)(2). However, this subsection shall not be construed as prohibiting the crossing of the center line in making a left turn into or from an alley, private road or driveway. (Acts 1980, No. 80-434, p. 604, §3-101.) .