116-121 Intersection


State Route 116/121 Intersection Improvement Project

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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). 


                  For a Visual Simulation of Roundabout: Click Image Below

Street ViewZoom In Map 



Aerial View
Current Configuration
Rendering of how the roundabout at the intersection of State Route 116 and State Route 121 would look.
Rendering of Completed Project