Authorized Emergency Vehicle.
An authorized emergency vehicle is:

• any vehicle of any fire department, police department, sheriff's office, coroner, prosecuting attorney, Washington State Patrol (WSP), or ambulance service, or
• any other vehicle authorized in writing by the WSP.

Authorized emergency vehicles using signal equipment consisting of a red visible light and a siren requires drivers to yield right-of-way and stop.
 
Tow Truck Lights.
Emergency tow trucks are required to have an identifying light that must: be red, revolve or flash intermittently, be visible from 360 degrees, and be visible from 500 feet under normal atmospheric conditions.  Emergency tow trucks must use the light at the scene of an emergency or accident.  A tow truck is not considered an authorized emergency vehicle and may not operate the light on the way to an accident or for any purpose other than at the scene of an emergency or accident.
 
Emergency Work Zone.
An emergency or work zone is defined as the adjacent lanes of the roadway 200 feet before and after an emergency or work zone vehicle.  The following vehicles qualify as emergency or work zone vehicles:

• a stationary authorized emergency vehicle that is making use of audible and/or visual signals that meet state requirements for authorized emergency vehicles;
• a tow truck that is making use of visual red lights that meet state requirements for emergency tow trucks;
• other vehicles providing roadside assistance that are making use of warning lights with 360-degree visibility;
• a police vehicle properly and lawfully displaying a flashing, blinking, or alternating emergency light or lights;
• or a stationary or slow-moving highway construction vehicle, highway maintenance vehicle, solid waste vehicle, or utility service vehicle that is making use of flashing lights that meet state requirements for snow-removal and other highway maintenance and service equipment or warning lights with 360-degree visibility.

 
Passing an Emergency or Work Zone.
If the highway has four or more lanes, at least two of which are intended for traffic proceeding in the same direction as the motor vehicle approaching the emergency or work zone, the driver of any motor vehicle must proceed with caution and, if the opportunity exists, with due regard for safety and traffic conditions, yield the right-of-way by making a lane change or moving away from the lane or shoulder occupied by an emergency or work zone vehicle. 
 
On a highway having fewer than four lanes, the driver of a motor vehicle must proceed with caution, reduce the speed of the vehicle, and, if the opportunity exists, with due regard for safety and traffic conditions, and following all applicable rules of the road, yield the right-of-way by passing to the left at a safe distance and simultaneously yield the right-of-way to all vehicles traveling in the proper direction on the highway. 
 
If changing lanes or moving away would be unsafe, the driver of a motor vehicle must proceed with due caution and reduce the speed of the vehicle to at least 10 miles per hour (mph) below the posted speed limit. 

Tow Truck Lights.
Emergency tow trucks may operate an intermittent or revolving red light when traveling to an emergency or accident.  Emergency tow trucks at the scene of an accident may use rear-facing blue lights.
 
Passing an Emergency or Work Zone.
Any driver who is unable to change lanes on a road passing an emergency or work zone and is proceeding with due caution in an adjacent lane is required to reduce the speed of the vehicle to 50 mph or lower when the posted speed limit exceeds 60 mph or more.