Welcome to Caltrans District 4

New 580/101 Connector Ramp

This project has been Completed

Traffic Shift on I-580/U.S. 101 Connector Ramp 7/18/10 PDF
Traffic Switch Graphic PDF

In mid-April, 2010, Caltrans will begin building a new connector ramp from westbound Interstate 580 to northbound U.S Route 101 in Marin County. Before the new ramp can be built, the old ramp must be demolished.

Traffic will be re-routed onto the ramp that connects southbound U.S. 101 to eastbound I-580. However, only one lane will be available in each direction. The reduction in capacity will lead to some congestion and delays. Drivers are asked to expect delays and adjust their commuting schedules.

Construction will last from April to October, 2010.


First opened in 1956, the connector ramp had only one lane for the first 53 years of its service life. Over the years, congestion steadily worsened. Caltrans and the Transportation Authority of Marin developed plans for a replacement structure.

However, in Spring 2009, Caltrans and TAM decided to re-stripe the existing ramp to two lanes, in order to provide some temporary relief for commuters. The re-striping was accomplished by eliminating the shoulders, which is permissible only on a temporary basis. At that time, both Caltrans and TAM emphasized that the restriping to two lanes was only temporary, and that a reduction back to one lane would be necessary to build the new ramp.

Features of the New Ramp

The new ramp will feature the following improvements:

Two lanes and two shoulders.
A flatter profile, resulting in improved sight distances.
A new auxiliary lane leading to the Bellam Boulevard off ramp.
Two lanes on the Bellam Boulevard on-ramp to northbound 101.
Improved traffic signals on Bellam Boulevard on and off ramps.
Significantly wider sidewalks on Bellam Boulevard and East Francisco Boulevard.

Here is a photo of the existing ramp, looking west on Bellam Boulevard:


Here is a computer-generated simulation of the new ramp:



Traffic on westbound 580 will be reduced to one lane roughly a quarter-mile from the existing ramp. Drivers will then be re-routed onto the existing eastbound connector ramp, then routed back over to westbound 580 just before the merge with northbound 101.

Traffic on southbound 101 will be reduced to one lane shortly after reaching the eastbound connector ramp.

Contact Information

For further information and updates, contact Caltrans Public Information Officer Bob Haus at:

(510) 286-5576


You can also get instant updates from our Twitter account at CaltransMarin.