Drivers who plan to use westbound State Route 18 in Federal Way late tonight should allow some extra time for their trips.

Crews working for the Washington State Department of Transportation (WSDOT) will close westbound SR 18 near Interstate 5 from 11 p.m. Wednesday to 4 a.m. Thursday.

A four-mile detour will direct drivers onto northbound I-5 to South 320th Street, then southbound I-5 to SR 18. Eastbound SR 18 will remain open.

During the closure crews will install form work for a future flyover ramp between westbound SR 18 and southbound I-5.

This work is part of a $112 million project to improve safety and ease congestion at the I-5/SR 18/SR 161 interchange. Crews are building two new flyover ramps to eliminate lane weaving that can lead to collisions. The new ramps are expected to open mid-2012.

For more information visit the project website.