Straight out of the Washington State Vehicle Code;
Left-Lane Restrictions
Any vehicle towing a trailer, or other vehicle or combination over
10,000 pounds, may not be driven in the left-hand lane of limited-access
roadways that have three or more lanes in one direction, excluding
HOV (high occupancy vehicle) lanes. This includes commercial trucks,
recreational vehicles, vehicles towing boats, and any car or truck towing
a trailer. Commercial vehicles over 10,000 pounds GVW are prohibited
from HOV lanes, even with the minimum number of occupants specified
on signs.
This law affects any limited-access roadway that has three or more
general purpose lanes in one direction. The law primarily affects
I-5, portions of I-90 and I-405 in King and Snohomish Counties,
and portions of I-90 in Spokane. It does not apply to HOV lanes, or to
drivers of affected vehicles who are preparing to turn left at an intersection, or exit onto a
private road or driveway. WSDOT will have signs posted in those areas where the law is in
affect. Failure to obey the law in areas where signs are posted will result in a citation by the
Washington State Patrol (WSP)
