The closure will be cover the entire 405 freeway in both directions over the Sepulvea Pass from late Friday evening, July 15, until early Monday, July 18. In other words, there will be no access on the 405 between the San Fernando Valley and the Westside.

The freeway is being shut down so that the south side of the Mulholland Bridge can be demolished; there will also be a full closure next year to tear down the northbound side of the bridge.

The work is part of the ongoing project to widen the 405 to add a carpool lane to the freeway between the 10 and 101 freeways, known officially as the I-405 Sepulveda Pass Improvements Project. The bridge will be rebuilt to accommodate a wider freeway. Other upgrades to the freeway are also being made.

Here’s how Supervisor Zev Yaroslavsky put it on his website:

“This is manageable as long as the public cooperates. They’ve got a lot of summer plans and we don’t want them to be surprised,” said Metro spokesman Marc Littman. “If you can stay home, great. If you don’t have to drive, great.” And if you do have to get behind the wheel, follow the officially marked detours, which by that point will have been widely publicized.

Metro will be launching a major p.r. blitz to keep the public informed and to give residents a chance to make other local travel plans. A press event is planned for next Monday early June and by next week more details will be released about detour routes.

It’s a huge deal, of course. About 500,000 vehicles travel that stretch of the 405 on a typical weekend.