116-121 Intersection

State Route 116/121 Intersection Improvement Project

Update November 14, 2024

Caltrans has been working since April 2024, constructing a roundabout at the intersection of Route 116/Route 121 and Bonneau Road in Sonoma County. The intersection was controlled with as four-way stop, which caused considerable congestion, especially after the northbound Route 121 to eastbound Route 121 bypass was closed during construction. 

On the morning of November 13, Caltrans removed the stop signs and opened the intersection as a roundabout.  Also, the northbound Route 121 to eastbound Route 121 was reopened. Motorists responded with little confusion and traffic congestion has decreased.  

The roundabout is not finished. But the current configuration roughly follows the pathway of the permanent design.  Caltrans will put construction on hold from mid-November until late February or even March because of the difficulty of working in the rainiest months. 

When construction crews return in 2025, they will add additional lanes to parts of the roundabout, stripe for pedestrian and bicycle passage, landscape, pave, add a bus top, sidewalks and other amenities. 

                                            ______________________________

Caltrans in conjunction with the Sonoma County Transportation Authority (SCTA) will begin construction on a project to build a roundabout at the intersection of State Route 116/121 in Lakeville, Sonoma County.  The $24 million project is scheduled to begin construction in fall 2023, with a completion scheduled for spring 2026.

Caltrans and SCTA studied several alternative designs before deciding upon a roundabout to solve the traffic concerns and alternative transportation issues ongoing at the intersection, ultimately choosing a roundabout over a signalized intersection. 

The Advantages of a Roundabout 

• Reduced congestion at intersection and an improved the level of service. 
• Reduced rates and severity of crashes due to fewer conflict points and lower traveling speed.
• Provides improved access to both pedestrians and bicyclists. 

Improvements to Existing Conditions

The current intersection lacks facilities for pedestrians and bicyclists. The new roundabout plan includes sidewalks on all sides and around the roundabout.  Similarly, the project will include improvements for cyclists.  Improved lighting will be added as well as pedestrian refuges and waiting areas for those waiting for the bus or fellow carpoolers. 

 Park and Ride Lot Relocation

 The existing Park and Ride lot will be relocated to the northeast of the new roundabout (see below).