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Highway 12-Jameson Canyon Road Widening Project

This Project Has Been Completed

Jameson Canyon Aerial


To safely accommodate the increasing number of motorists traveling between Napa and Solano Counties, Caltrans is working with the Napa County Transportation and Planning Agency (NCTPA) and the Solano Transportation Authority (STA) to widen a 5.8-mile stretch of State Route 12 through Jameson Canyon Road from a two-lane highway to a four-lane highway. The project extends from Highway Route 12 from the Highway 29 & Highway 12 junction in Napa County to Red Top Road & Highway 12 in Solano County. The project will also add a concrete median along the project route. Once completed, the project will improve safety and travel times throughout the region.

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Safety improvements for the Route 12 project includes:

  • Widening Route 12 from a two-lane highway to four within the 5.8-mile stretch
  • Constructing a concrete median along the project’s 5.8-mile stretch
  • Improving sight distance
The Highway 12-Jameson Canyon Road Widening Project includes two construction packages; The Napa County contract and the Solano County contract. The project is funded by the Corridor Mobility Improvement Account (CMIA), the State Transportation Improvement Program (STIP), and Proposition 1B. The entire project will cost approximately $115 million.

Weather permitting the entire project could be completed as early as summer 2014.

The majority of construction work is scheduled for after April 1st 2012, between the hours of 11:00 p.m. and 5 a.m. During this time, Caltrans will schedule overnight closures to State Route 12 with alternative routes posted. Motorists are advised to expect delays during partial closures and will be directed to alternate routes during full closures.

Detour Map

Caltrans posts Commuter Advisories regarding the Highway 12-Jameson Canyon Widening Project on our Caltrans District 4 Website at: http://www.dot.ca.gov/dist4/

Twitter – SR12-Jameson Canyon Twitter

The Twitter page is updated as needed with information regarding closures and/or detours in the area.

The URL below is a link to the 2008 environmental documents pertaining to the Route12-Jameson Canyon Road Widening Project:


The Highway 12-Jameson Canyon project passed the guidelines for the California Environmental Quality Act (CEQA) and the National Environmental Policy Act (NEPA) in January 2008.


Vince Jacala
Caltrans District 4
Public Affairs 510-286-5206