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 require drivers to yield right-of-way and stop.
 
All fire department vehicles in service are identified by intermittent flashing red lights, visible from both front and rear for a distance of 500 feet under normal atmospheric conditions.  The red flashing lights must be separated from the headlights so that they do not black out when the headlights are on.  The red flashing lights must be in operation at all times when such vehicle is on emergency status.
 
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.

The rules of the road provide specific rules for 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.

Fire department vehicles may operate rear-facing blue lights.  The combination of red and blue lights shall only be used at the scene of the emergency.

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 no more than 50 mph when the posted speed limit exceeds 60 mph or more.