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101 Tamalpais Overcrossing

Tamalpias Overcrossing UPDATES
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Caltrans will be replacing the fill layer beneath the asphalt at the approaches for both sides of the Tamalpais Drive Overcrossing (post mile 7.37), over US Route 101, in Corte Madera of Marin County. The current fill layer, consisting predominately of gravel and sand, has experienced settlement due to stormwater damage, causing embankments to become uneven and damaged. The replacement fill material of cellular concrete; a pre-mixed slurry of hydraulic concrete, water, and pre-formed foam, will provide greater structural stability.

The Tamalpais Drive Overcrossing project involves:

  • Excavating a 10 to 15-foot depth of fill layer material and replacing it with cellular concrete.
Additionally, there will be minor construction work in the area adjacent to the Tamalpais Drive Overcrossing. This involves:
  • Construction of new sidewalks and minor upgrades to traffic signal loops.
The contract for the project was awarded to Ghilotti Construction Company, with construction costs totaling $1,234,000. Construction work began end of May with the goal of completion by mid September, weather permitting.


This project was cleared under categorical exemption/categorical exclusion. No agency permits were required.


Caltrans has scheduled overnight closures between the on/off ramps along Tamalpais Drive Overcrossing during construction. On/off ramp closure is necessary because the excavation/shoring/concrete pours are directly in the intersection where the ramps meet Tamalpais. Once the excavation, sheet piling, and concrete pours are completed, there will be one lane open in each direction for miscellaneous work (concrete curb/gutter and signal work). Work involving concrete will be weather dependant. Motorists will not be permitted on the roadway and alternative routes will be posted.

Monday evening – Thursday evening: 10 pm to 6 am (following morning)
Friday evening: 10pm to 8 am (Saturday)

Minor construction work, consisting of sidewalk and traffic signal loop upgrades, will occur in the area adjacent to the Overcrossing. This work is also scheduled for overnight closures, and should have no effect on Highway 101 traffic.

Monday – Friday: 7 pm to 6 am
Saturday & Sunday: 7 pm to 11 am

Daytime traffic is not anticipated to be effected during either type of construction work.


During construction, motorists will be prompted to use one of the five detours below, depending on the work being done that particular night. Please consult the ‘Traffic Advisories’ section of this Project Page to determine which detour will be in affect.

Detour #1

Full Closure: Work on the south side of the bridge approaches simultaneously. Close
Eastbound Tamalpais lane to northbound Route 101.
This detour is similar to detour #3 below, but traffic can also use Southbound 101 to Tiburon
Blvd to merge onto Northbound 101 and head north to destination, if wanting to go
Northbound 101 and not just cross onto the east side of Route 101.

Detour #2

Full Closure: Work on the north side of the bridge approaches simultaneously. Close westbound Tamalpais Lane to southbound Route 101.
Similar to detour #1, but traffic can also use Northbound 101 to Sir Francis Drake Blvd to merge onto Southbound 101 and head south to destination if wanting to go Southbound 101 and not just cross onto the west side of Route 101.

Detour #3

Full Closure: Work on the west side of the bridge only. Close eastbound lane onto bridge and detour traffic.
Traffic on Tamalpais Dr. will not be able to cross bridge, but will be able to use Redwood Hwy. and Tamalpais Dr. on either sides to cross on Wornum.

Detour #4

Full Closure: Work on the east side of the bridge only. Close westbound lane onto bridge and detour traffic.
Northbound traffic exiting at Tamalpais Dr. turns north onto Redwood Hwy and crosses to the west side of Route 101 using Wornum Dr., then heads south on Tamal Vista Blvd. and further south onto Madera Blvd. to reach Tamalpais Dr.

Detour #5

Full Closure: Work on both sides of the bridge simultaneously. Tamalpais Dr. Route 101-Northbound/Southbound. Off-ramp closure and detour traffic.
Northbound traffic continues north and exits at Lucky Drive then heads south on Redwood Hwy. to Tamalpais Dr.
Southbound traffic exits at Madera Blvd. and heads south to Tamalpais Dr.


For traffic advisories pertaining to the Tamalpais Drive Overcrossing project, please see the Caltrans District 4 website at www.dot.ca.gov/dist4

Frequently Asked Questions

1. Why does Caltrans feel it is necessary to build this project?

Thick settlement has caused an uneven ride on and off the bridge deck, causing safety concern.

2. What measures did Caltrans consider to minimize the economic impacts on the adjacent Shopping malls?

Caltrans decided to rehabilitate the Tamalpais Drive Overcrossing outside of holiday the season.

3. What measures did Caltrans consider to minimize the traffic impacts on the 101 and the adjacent cities?

The project is located within a high intensity shopping district where traffic impacts would be felt in the City of Corte Madera and also upon neighboring cities all the way to the City of Larkspur and Mill Valley. With the help of the cities puplic work directors and CHP’s we develpoed detroures to minimize traffic impacts.

4. What is the anticipated time frame for this project?

Caltrans awarded this project to a private contractor on 3/27/12 and we anticipate this project beginning by June 2012 and ending by August of 2012.