Both directions of the State Route 99 tunnel in Seattle will close for scheduled maintenance 10 p.m. Friday, Dec. 1 until 6 a.m. Saturday, Dec. 2.

The tunnel closure will allow the Washington State Department of Transportation to conduct several important tasks, including:

• Mechanics will conduct fire extinguisher inspections; fire sprinkler visual inspections; lubricate and test the jet fans; and visual and audible inspections of the roadway and ventilation dampers.

• Technicians will perform seasonal maintenance on roadway fire systems.

• Electronic crews will replace some cameras and calibrate the haze detectors.

• WSDOT signals crew will clean the variable message signs and cameras and repair lighting in the tunnel.

People traveling through the area Friday night should use alternate routes. Find real-time travel information via the WSDOT mobile app and the real-time travel map.