101 Deck Replacement project at Alemany Circle in San Francisco

101 alemany fact sheet banner

Caltrans will replace 800-feet of bridge deck on US 101 just north of the Alemany Boulevard exit in San Francisco. During the project the bridge deck of the freeway will be demolished and rebuilt, which will require detouring freeway traffic on and off the freeway to provide room for construction. The project will begin in July 2020 and be finished within three weeks.

SB101 Video Image Deck Replacement

This portion of the US 101, sometimes referred to as the Bayshore Freeway, was built in the early 1950s. Over the past 70 years, weather and heavy traffic have deteriorated the bridge deck to the point where replacement is the most feasible option.

A bridge deck is a large, concrete and steel box which sits on top girders spanning the space between bridge columns.

location of alemany deck replacement project

Roadway Conditions

Workers build wooden forms to hold wet concrete, which they lay atop steel girders. A steel lattice is built on top the forms over which they pour concrete. The concrete hardens into a sturdy bridge deck. The process used when this bridge was built is not very different from the process used today.

In the case of the Alemany Deck Replacement Project, Caltrans complete the demotion and rebuilding of the northbound lanes before moving onto
picture of a bridge with concrete removed

If it weren’t for traffic, the process of replacing the deck would be straight-forward. but it’s 70 years too late for such a luxury. Today, over 160K vehicles pass over the Alemany bridge deck each day. Accommodating traffic will be the most challenging part of the project.

To provide room to build the project, Caltrans will build a detour that will take northbound US 101 traffic off the freeway at the Alemany Boulevard exit.  Traffic will travel about 600 feet and re-enter the freeway at the Northbound US 101 on-ramp.

This short detour will clear northbound US 101 of traffic, allowing work crews to demolish and rebuild the bridge deck on northbound 101.

Fact Sheet

Frequently Asked Questions

Project Contact

Caltrans Public Information Officer
Jose Moreno-Jimenez