§ 20‑146. Drive on right side of highway; exceptions.
(a) Upon all highways of sufficient width a vehicle shall be driven upon the right half of the highway 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 so doing 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 highway divided into three marked lanes for traffic under the rules applicable thereon; or
(4) Upon a highway designated and signposted for one‑way traffic.
(b) Upon all highways any vehicle proceeding at less than the legal maximum speed limit shall be driven in the right‑hand lane then available for thru traffic, or as close as practicable to the right‑hand curb or edge of the highway, except when overtaking and passing another vehicle proceeding in the same direction or when preparing for a left turn.
(c) Upon any highway 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 centerline of the highway, except when authorized by official traffic‑control devices designating certain lanes to the left side of the center of the highway for use by traffic not otherwise permitted to use such lanes or except as permitted under subsection (a)(2) hereof.
(d) Whenever any street has been divided into two or more clearly marked lanes for traffic, the following rules in addition to all others consistent herewith shall apply.
(1) A vehicle shall be driven as nearly as practicable entirely within a single lane and shall not be moved from such lane until the driver has first ascertained that such movement can be made with safety.
(2) Upon a street which is divided into three or more lanes and provides for the two‑way movement of traffic, a vehicle shall not be driven in the center lane except when overtaking and passing another vehicle traveling in the same direction when such center lane is clear of traffic within a safe distance, or in the preparation for making a left turn or where such center lane is at the time allocated exclusively to traffic moving in the same direction that the vehicle is proceeding and such allocation is designated by official traffic‑control device.
(3) Official traffic‑control devices may be erected directing specified traffic to use a designated lane or designating those lanes to be used by traffic moving in a particular direction regardless of the center of the street and drivers of vehicles shall obey the direction of every such device.
(4) Official traffic‑control devices may be installed prohibiting the changing of lanes on sections of streets, and drivers of vehicles shall obey the directions of every such device.
(e) Notwithstanding any other provisions of this section, when appropriate signs have been posted, it shall be unlawful for any person to operate a motor vehicle over and upon the inside lane, next to the median of any dual‑lane highway at a speed less than the posted speed limit when the operation of said motor vehicle over and upon said inside lane shall impede the steady flow of traffic except when preparing for a left turn. "Appropriate signs" as used herein shall be construed as including "Slower Traffic Keep Right" or designations of similar import. (1937, c. 407, s. 108; 1965, c. 678, s. 2; 1973, c. 1330, s. 3; 1975, c. 593; 1985, c. 764, s. 25; 1985 (Reg. Sess., 1986), c. 852, s. 17; 2001‑487, s. 11.)