To: Board of Supervisors
From: Warren Lai, Public Works Director/Chief Engineer
Report Title: Accepting and Declaring a Certain Road as County Road (a portion of Mt. Diablo Scenic Boulevard), Mt. Diablo Scenic Boulevard and Diablo-Blackhawk Road Intersection Signal Improvements Project No. 0676-6P1106 (cross-reference RA24-01259), Diablo area.
Recommendation: Recommendation of the County Administrator
RECOMMENDATIONS:
ADOPT Resolution accepting and declaring a Certain Road as County Road (a portion of Mt. Diablo Scenic Boulevard), Mt. Diablo Scenic Boulevard and Diablo-Blackhawk Road Intersection Signal Improvements Project No. 0676-6P1106 (cross-reference RA24-01259), as recommended by the Public Works Director, Diablo area. (District II)
FISCAL IMPACT:
No fiscal impact
BACKGROUND:
Davidon Homes is constructing the Magee Preserve project, a subdivision development located in the Town of Danville. The subdivision development (69 single family homes and seven ADUs) is located nearby and generally south of the Mt. Diablo Scenic Boulevard and Diablo-Blackhawk Road intersection which is located in unincorporated Contra Costa County. The Town of Danville oversaw the entitlement process, including the approval of the final environmental impact report, which required off-site improvements including the installation of a new traffic signal at the subject intersection, which was stop sign-controlled.
Davidon designed and installed a traffic signal at the subject intersection in accordance with the required condition of approval of their subdivision development project. Davidon began working with the County Public Works Department on the design of the traffic signal to ensure vehicle and pedestrian safety. As part of this process, Davidon and the County identified operational improvements (primarily adding a right turn lane at the traffic signal) that were beyond the scope of the condition of approval. The County agreed to obtain public roadway easements for a portion of Mt. Diablo Scenic Boulevard (private road) to construct these operational improvements to allow the proposed traffic signal to work more efficiently. These proposed improvements beyond the installation of the traffic signal will be reimbursed by the County as its cost contribution toward the overall project. The signal and operational improvements were constructed in August 2026, and a Notice of Completion of the construction project was filed with the Board of Supervisors at its October 6, 2026, meeting.
The County will accept a portion of Mt. Diablo Scenic Blvd. that starts at its intersection with Diablo/Blackhawk Road to approximately 280 feet north of the intersection. This includes the portion of Mt. Diablo Scenic Blvd. that includes the new southbound right-turn lane and its transition to the remaining two lane private road. The northerly limit of the County’s maintained roadway is just south of the existing twin storm drain culvert pipes under Mt. Diablo Scenic Blvd. (these culvert pipes are not maintained by the County).
CONSEQUENCE OF NEGATIVE ACTION:
The road will not be part of the County Maintained Roads system and the County will not be eligible for State gas tax funds.
c: Jocelyn LaRocque-Engineering Services, Larry Theis-Engineering Services, Renee Hutchins-Records, Theresa Shepherd-Design & Construction, Chris Lau-Transportation, Walid Gardizi-Finance, Joanne Bohren-Auditor, David Homes