The Law

Not sure what RCW 46.61.100 actually means? Read below, it is direct from the WA State Legislature of all permanent laws now in force.

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

(a) When overtaking and passing another vehicle proceeding in the same direction under the rules governing such movement;

(b) 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;

(c) Upon a roadway divided into three marked lanes and providing for two-way movement traffic under the rules applicable thereon;

(d) Upon a street or highway restricted to one-way traffic; or

(e) Upon a highway having three lanes or less, when approaching a stationary authorized emergency vehicle, tow truck or other vehicle providing roadside assistance while operating warning lights with three hundred sixty degree visibility, or police vehicle as described under *RCW 46.61.212(2).

(2) Upon all roadways having two or more lanes for traffic moving in the same direction, all vehicles shall be driven in the right-hand lane then available for traffic, except (a) when overtaking and passing another vehicle proceeding in the same direction, (b) when traveling at a speed greater than the traffic flow, (c) when moving left to allow traffic to merge, or (d) when preparing for a left turn at an intersection, exit, or into a private road or driveway when such left turn is legally permitted. On any such roadway, a vehicle or combination over ten thousand pounds shall be driven only in the right-hand lane except under the conditions enumerated in (a) through (d) of this subsection.

(3) No vehicle towing a trailer or no vehicle or combination over ten thousand pounds may be driven in the left-hand lane of a limited access roadway having three or more lanes for traffic moving in one direction except when preparing for a left turn at an intersection, exit, or into a private road or driveway when a left turn is legally permitted. This subsection does not apply to a vehicle using a high occupancy vehicle lane. A high occupancy vehicle lane is not considered the left-hand lane of a roadway. The department of transportation, in consultation with the Washington state patrol, shall adopt rules specifying (a) those circumstances where it is permissible for other vehicles to use the left lane in case of emergency or to facilitate the orderly flow of traffic, and (b) those segments of limited access roadway to be exempt from this subsection due to the operational characteristics of the roadway.

(4) It is a traffic infraction to drive continuously in the left lane of a multilane roadway when it impedes the flow of other traffic.

(5) Upon any roadway having four or more lanes for moving traffic and providing for two-way movement of traffic, a vehicle shall not 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 (1)(b) of this section. 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.

http://apps.leg.wa.gov/rcw