County Of Sonoma › Development Services › Sonoma Public Infrastructure › Roads: Projects & Services › Road Resources

Road Resources

close-up image of a construction vehicle

Sonoma County Public Infrastructure provides a wide range of resources to guide contractors, developers, and the public in understanding and working within the County road system. These resources include the County’s Functional Classification system, which defines how roads are categorized (local roads, collectors, arterials), the official Construction Standards Library (designs and technical notes contractors must follow), and 18 interactive maps covering topics such as road closures, pavement condition, bridges, and traffic volumes.

Together, these tools ensure that road construction, maintenance, and development projects are safe, efficient, and consistent with County and state requirements.

Functional Classification of Roads

Roads in Sonoma County are categorized using the Functional Classification system, developed by the Federal Highway Administration and applied by Caltrans. This system organizes roads based on traffic volume, connectivity, and purpose, helping determine how they are designed, maintained, and funded.

ARTERIALS		Carry the highest volumes of traffic and connect major communities.
	Interstates:	Long-distance, high-speed highways with limited access. None exist within Sonoma County.
	Freeways & Expressways:	Similar to interstates but serve regional rather than national travel. Examples: US Highway 101 and State Highway 12 (not County-maintained).
	Other Principal Arterials:	Connect metropolitan areas and allow direct land access through intersections or driveways.
	Minor Arterials:	Serve shorter trips, provide community connections, and may carry local bus routes.
COLLECTORS		Collectors gather traffic from local roads and feed it into the arterial network.
	Major Collectors:	Longer routes with higher speeds, traffic volumes, and eligibility for federal funding.
	Minor Collectors:	Shorter routes with lower speeds and traffic volumes; not eligible for federal funding.
LOCAL ROADS		Local roads make up most of the County’s road mileage. They provide direct property access, discourage through-traffic, and typically do not support bus routes.

Construction Standards

Series 100-219E: Roadway

Series 220-229: Sidewalk

Series 230-242: Fencing

Series 300: Mail & Newspaper Boxes

Series 400: Drainage

Series 600: Streetlights

Series 700: Traffic Signing

Series 800: Driveways

Series 900: Design

map of Lake Sonoma

Collection of Interactive Maps

We are excited to offer the public a collection of interactive maps that make it easier to explore, understand, and engage with Sonoma County’s roadways and infrastructure. These tools provide valuable, real-time information ranging from road conditions to community involvement programs. Popular highlights include the Adopt-a-Road Program Map, which showcases roads cared for by local volunteers; the Road Closures and Delays Map, offering up-to-date information on closures and construction; and the Pavement Condition Map, which shows inspection-based roadway quality across the county. Other favorites, such as the Planned Paving Projects Map and the Speed Limits Map, allow residents to stay informed about improvements and safety measures in their communities.

Interactive Maps