Arizona Department of Transportation crews are detouring traffic on Interstate-40 this week in Flagstaff as workers continue working on the Fourth Street Bridge project. Westbound I-40 is being detoured beginning through 6 p.m. Thursday. During the closures on I-40, there will be short, intermittent lane closures on the Fourth Street Bridge. Flaggers will stop traffic and direct motorists through the work zone during lane-closures, which should be less than 15 minutes at a time. The closures are needed as crews begin to install girders on the bridge. Girders are the concrete beams that provide the main horizontal support for the bridge deck.