Skip to Content | Accessibility Assistance | Resize Text: decrease font size increase font size reset

Highway 101 Congestion Relief Program

Highway 101 Widening Projects Phasing Strategy Map
PDF Icon101 Project Map

Highway 101 through most of Sonoma County was constructed between 1954-1962. It is the primary north – south corridor through the county. A 1958 traffic count at the College Avenue interchange indicated that 15,000 cars a day were using the freeway (at that segment). A 2006 Caltrans traffic count at the same location found that over 125,000 cars a day were traveling on the same four-lane freeway. Planners in the 1950's envisioned a freeway widened to six lanes in the 1970s to handle projected population growth in Sonoma County. However, as the population grew, the improvements lagged severely behind.

It is a goal of the SCTA to create a safe, convenient, free flowing Highway 101 with a less intense rush hour period where traffic moves at a steady pace. To reach this goal, SCTA developed a program of six Highway 101 HOV projects that would not only create a continuous HOV lane from the Sonoma County line to Windsor, but would also address operational and safety problems throughout the corridor. A separate environmental document for each HOV project has been certified.

Below is the detail on the various phases of work, but the status of the work yet to be completed can be found here: PDF IconStatus of Current Highway 101 Projects

The following projects are part of the Sonoma County Transportation Authority's 2004 Comprehensive Transportation Plan and are included in the Highway 101 Congestion Relief Program for Sonoma County. These projects will improve traffic operations and provide continuous High Occupancy Vehicle (HOV) lanes between southern Marin County and Windsor in Sonoma County.

1) South Santa Rosa (Santa Rosa Avenue to Highway 12)
This project has been constructed and approximately 4.6 miles of HOV lanes in each direction are open to traffic in southern Santa Rosa. Ramp metering will be implemented as a separate contract, once adjacent projects are complete. The environmental document for this project can be found at: http://www.dot.ca.gov/dist4/sonoma101/SON101.html

2) Downtown Santa Rosa (Highway 12 to Steele Lane)
The major phase of this project has been constructed which added approximately 2.5 miles of HOV lanes in each direction. Ramp improvements and auxiliary lanes were also provided to encourage HOV use and improve mainline traffic operations. The project included new structures; structure replacement and improvements; sound wall construction; intelligent transportation systems, including ramp metering; and modification to the surrounding local street network to improve local circulation and access. Subsequent phases to widen College Avenue and connect 6th Street under the new freeway bridge are under development. A follow-up landscaping project is scheduled to go to construction in late 2015.

The Caltrans website for this project is located at: http://www.dot.ca.gov/dist4/son101/

The environmental document for the Downtown Santa Rosa project can be found at: http://www.dot.ca.gov/dist4/son101/101hovdocuments.htm

3) Wilfred (Rohnert Park Expressway to Santa Rosa Avenue)
This project added approximately 1.6 miles of HOV lanes in each direction. It also included auxiliary lanes between the Rohnert Park Expressway and Wilfred Avenue Interchanges, a southbound collector/distributor road between Santa Rosa Avenue and Wilfred Avenue, ramp improvements, an expansion of an existing park-and-ride lot, modifying the local street network (including a direct connection from Golf Course Drive to Wilfred Avenue) to improve access and circulation, and intelligent transportation systems, including ramp metering. The Wilfred project started construction in early 2009 and was completed in June 2013. A follow-up landscaping project is planned, but not yet funded.

The Caltrans website for this project is located at: http://www.dot.ca.gov/dist4/wilfredave/

The environmental document for the Wilfred project can be found at: http://www.dot.ca.gov/dist4/envdocs.htm#wilfred

4) North (Steele Lane to Windsor River Road)
This project added approximately 7.5 miles of HOV lanes in each direction. The project has been split into three phases, A, B, and follow-up landscaping.

Phase A extended HOV  for 7.5 miles, from Steele Lane in Santa Rosa to Windsor River Road in Windsor. It also provided ramp improvements, a complete rehabilitation of the roadway, and intelligent transportation systems including ramp metering. Phase A started construction in late 2008 and was completed in 2010.

Phase B includes interchange improvements to the Airport Boulevard and Fulton Road interchange complex including a new, wider Airport Boulevard Overcrossing. The Highway 101 ramps at Fulton Road will be closed to avoid operational (merging) problems caused by the two closely spaced intersections. Additionally, the project will also construct sound walls at various locations in the Town of Windsor. Construction began on the North-B project in October, 2012 and was completed, ahead of schedule, in June 2013. http://www.dot.ca.gov/dist4/101airportblvd/

A follow-up landscaping project is planned to begin construction in 2016.

The environmental document for the North project can be found at: http://www.dot.ca.gov/dist4/envdocs.htm#101hovson

5) Central (Old Redwood Highway in Petaluma to Rohnert Park Expressway)
This project added approximately 6.4 miles HOV lanes in each direction. The project has been split into three phases, A, B, and C.

Phase A includes construction of the HOV lanes from just north of Pepper Road in Petaluma to Rohnert Park Expressway, in Rohnert Park. It also includes auxiliary lanes, soundwalls in Cotati, ramp improvements, a rehabilitation of the roadway north of Railroad Avenue, and intelligent transportation systems, including ramp metering. Phase A is fully funded. Phase A started construction in 2010 and is was completed in 2012.

Phase B includes the construction of the HOV lanes from just south of Old Redwood Highway in Petaluma to just north of Pepper Road. It also includes ramp improvements, a soundwall in Petaluma, and a rehabilitation of the roadway. Phase B started construction in 2011 and was completed in 2013.

Phase C will construct a new Old Redwood Highway (Petaluma Boulevard North) interchange, including a replacement of the Highway 101 overcrossing bridge. The ramps will be re-aligned and provide HOV bypass lanes and ramp metering. This project also proposes to build a portion of the soundwall that connects the Phase B soundwall. Project  construction started in Spring, 2013 and is expected to be completed in 2015.

A follow-up landscaping project is planned, but not yet funded.

The environmental document for the Central project can be found at: http://www.dot.ca.gov/dist4/envdocs.htm#101hovorh

Sonoma Marin Narrows Map
PDF IconMarin-Sonoma Narrows Map

6) Marin/Sonoma Narrows (MSN) (Highway 37 in Novato to Old Redwood Highway in Petaluma)
This project will add approximately 17 miles of HOV lanes in each direction. The project also includes new structures; structure improvements; intelligent transportation systems, including ramp metering; and soundwalls. The project would also upgrade the 9-mile long "Novato Narrows" section from expressway to freeway. It would provide interchanges and frontage roads to replace eighty (80) at grade intersections and driveways, and would replace the San Antonio Creek Bridge, which is prone to flooding and major highway closures. It would also improve horizontal and vertical alignment, in order to bring the facility to freeway standards. This project will be constructed in phases. The following initial phases have been identified:

Phase I Projects: The following four fully funded projects are considered the MSN Phase I projects.

Phase A1 will construct a northbound HOV lane from State Route 37 to just north of Atherton Avenue and a southbound HOV lane from SR 37 to Rowland Boulevard in Marin County. It will also construct soundwalls, and intelligent transportation systems, including ramp metering. Phase A-1 is fully funded. This project started construction in 2011 and was completed in 2012.

Phase A2 will construct a southbound HOV lane from Novato Creek to Franklin Overhead in Novato and was completed in 2013.

Phase A3 will extend the northbound HOV lane from Atherton Avenue to 1.5 miles south of the new Redwood Landfill Interchange. Construction on Phase A3 began in 2012 and was substantially completed by end of 2014.

Phase B1 will convert the Redwood Landfill overcrossing into a full interchange and add frontage roads. The new frontage roads will eliminate existing direct access from San Antonio Road and driveways and include Class I & II bicycle facility. By implementing access control within the contract limits, the facility will ultimately be converted from expressway to freeway. Construction started on Phase B-1  in 2012 and is expected to be completed in 2015.

Phase B2 will construct a new Petaluma Boulevard South interchange and overcrossing, south of the existing interchange. Kastania Road will be lengthened to the north and the south and will connect to the new interchange location. Petaluma Boulevard South will be re-aligned, lengthened, and widened for a Class II bike lane. The frontage Roads will allow implementation of access control within the contract limits, so the facility can ultimately be converted from expressway to freeway. Phase B-2 also replaces the existing two Highway 101 bridges over Petaluma River with a new 6-lane bridge. The highway profile is corrected to improve site distance and widened between the Petaluma River Bridge and the new interchange location. Phase B-2 is started construction in 2012 and is expected to be completed by 2016. http://www.dot.ca.gov/dist4/101petalumablvd/

Phase B3 will realign Highway 101 to the west, in the vicinity of the San Antonio Creek at the Sonoma - Marin County Line. The project will construct a new 6-lane Highway 101 bridge over San Antonio Creek and improve sight distance and resolve flooding issues at this location. This project will extend the Petaluma Boulevard South frontage road to the County Line, including Class II bike lanes. A new Class I bike lane will be constructed along San Antonito Creek to connect facilities on the west and east side of the highway. Phase B-3 is expected to start construction in 2015 and be completed by 2017.

Phase C1 Considered a part of the Marin/Sonoma Narrows (MSN) project, Phase C1 has been environmental cleared as part of a separate document to advance delivery. The project will improve ramps at the East Washington interchange in Petaluma. It will correct the ramp geometry of the southbound on-ramp and will provide a new on-ramp from westbound East Washington Street to northbound Highway 101 in order to help local circulation in Petaluma. The East Washington project started construction in 2011 and was completed in 2014.

Phase C2 will construct HOV lanes in both directions from just north of Route 116 (East) to Old Redwood Highway (Petaluma Boulevard North) in Petaluma. This project will widen bridges, replace the North Petaluma Overhead Bridge, construct soundwalls in Petaluma, and provide intelligent transportation systems, including ramp metering. This project has been completed to 95% design in 2014. The challenges for future years will include obtaining funds to complete remaining MSN HOV lanes and landscaping the entire corridor.

Phase C3 will replace the existing southbound bridge over Route 116 (East) with a 3-lane bridge and widen the existing northbound bridge to accommodate future HOV lanes. This project will also improve the northbound ramps at the Route 116 (East) separation, including a HOV bypass lane and ramp metering. A soundwall is included in Petaluma on the NB on-ramp from Route 116 (East). Phase C3 construction began  in 2012 and is expected to be completed by 2015.

Future Phase Projects: Future phases of the MSN project are under-development. SCTA is advancing the design of the following two future phase projects. Additional phases to complete the overall MSN project are also being considered.

Sonoma Phase 2 - Median Widening This project will widen Highway 101 for HOV between the Marin County Line and the new Petaluma Boulevard South Interchange. This project is funded through design and a schedule is being developed to ready the project for construction funding opportunities.

Other Phases The Transportation Authority of Marin (TAM) is working with Caltrans to develop the remaining phases to complete the Highway 101 HOV lanes between Novato and the Sonoma County Line. There is also a follow-up landscaping project scheduled for 2015.

The Caltrans website for the MSN project is located at: http://www.dot.ca.gov/dist4/msn/

The draft environmental document for the MSN Corridor project can be found at: http://www.dot.ca.gov/dist4/envdocs.htm#msnhov

The separate environmental document for the East Washington project can be found at: http://www.dot.ca.gov/dist4/envdocs.htm#101ew

Some documents on this web site are saved in Portable Document Format (PDF). We recommend you download Adobe® Reader®, a free software that lets you view and print PDF files.