The goals of this $56-million project in the heart of San Rafael were to elevate and widen the northbound and southbound Highway 101 lanes for the addition of HOV (high occupancy vehicle) lanes and to construct a new southbound 101/eastbound Interstate 580 connector.

One of the more innovative aspects of the project’s design was the use of both lightweight aggregates and EPS block (expanded polystyrene). The project is located immediately adjacent to the San Francisco Bay, so much of the native material underneath the site is what is referred to as “bay mud.” This material is very fluid and tends to not compact very well. Over time, the material displaces due to the weight of the structural section and live loads above, causing settlement on the surface. To counter these effects, the project was designed to incorporate the use of lightweight materials, which would reduce the amount of weight in the structural section, thereby causing less displacement of the native material below.