Website Header Spotlight

The header for the Western District’s website this quarter features a photo of the Sonoma County Agua Caliente Roundabout.  The following is an article written by Zack Matley of W-Trans regarding this project.

Written By: Zack Matley, AICP

The County of Sonoma, California, is faced with serving increasing vehicle traffic volumes on two-lane County roads at low-capacity intersections.  One such location was the intersection of Arnold Drive/Agua Caliente Road in the Sonoma Valley; Arnold Drive parallels CA State Highway 12 and provides and alternate route for area traffic.  The intersection is located at the junction of two arterials in the community of Agua Caliente, at the transition between rural and suburban areas.  The all-way stop controls that previously existed resulted in significant delay and queuing on Arnold Drive.  A roundabout was determined to be the optimal improvement to the intersection and was funded jointly by the County of Sonoma and Hanna Boys Center, whose access is the western leg of the roundabout.  Hanna Boys Center is a residential treatment center with an on-campus accredited school, serving 8th through 12th grade students.

W-Trans of Santa Rosa and Oakland was responsible for the horizontal design of the roundabout, roundabout signing and striping plans, electrical plans, traffic handling plans, roundabout traffic analysis, and support on related issues including landscaping design.  Civil engineering design, drainage improvements, utility relocations, and related work was completed by the prime consultant, Brelje & Race of Santa Rosa.

Key design constraints included the need to regulate entering vehicle speeds on Arnold Drive, avoid right-of-way impacts, minimize environmental impacts associated with trees and street lighting, and accommodate a major utility vault outside of the circulating lane.  Construction of the roundabout was completed in December 2013.  Since that time, queuing on Arnold Drive and delay at the intersection have diminished and speeds have been maintained at desirable levels.

W-Trans has used drones to monitor the circulation and operation of the roundabout as shown in the photo.


Photo Credit:  Kameron Flores-Maxfield (via drone)