State Routes 9, 35, and 84 (Four Corners) Safety Improvements in San Mateo County

Caltrans is committed to improving safety along State Routes 9, 35 and 84 in San Mateo County. As part of ongoing efforts toward a goal of zero traffic fatalities and serious injuries on all California public roadways by 2050, Caltrans has completed several traffic safety investigations and is implementing a series of improvements at the intersection of State Route 35 (Skyline Boulevard) and State Route 84 (La Honda Road), commonly known as the Four Corners Intersection.

These improvements are intended to enhance safety for motorists, pedestrians and bicyclists while improving traffic mountain intersections.

Why Improvements Are Needed

Traffic safety evaluations identified the Four Corners Intersection as an area where:

• Vehicle collision rates are higher than statewide averages for similar intersections.
• A significant number of reported collisions involve improper turning movements.
• Additional measures can improve visibility, traffic control and pedestrian and bicycle safety.

Based on these findings, Caltrans developed a phased approach to implement both immediate and near-term safety improvements.

Safety Improvements Already Completed

Over the past two years, Caltrans has conducted several traffic safety investigations along State Routes 9, 35 and 84 in San Mateo County to identify opportunities for traffic calming and safety enhancements.

These investigations evaluated improvements such as:

• New and upgraded traffic signs
• Enhanced pavement striping and markings
• Speed reduction measures
• Red curb painting
• High-visibility crosswalks

Nearly half of the recommended safety measures identified through these investigations have already been implemented. One of these investigations resulted in immediate and near-term improvements at the Four Corners Intersection.

Caltrans District 4's Safety Team additionally met with the Town of Woodside Circulation Committee to provide an update on planned improvements and implementation timelines.

Construction on the Four Corners Intersection is scheduled for completion in August 2026 and includes:

• Painting curbs red at four locations to improve intersection visibility and reduce parking conflicts.
• Enhancing the north crosswalk with high-visibility ladder striping.
• Installing yield line pavement markings at the north crosswalk.
• Installing "KEEP CLEAR" pavement markings to improve intersection operations.
• Refreshing existing pavement striping and markings where needed.

Near-Term Safety Improvements

Construction is anticipated to occur between August and October 2026.

Planned improvements include:

• Enhancing pavement striping and lane delineation throughout the intersection.
• Installing all-way STOP pavement markings.
• Converting the intersection to all-way STOP control with new stop signs.
• Installing a new pedestrian crossing.
• Upgrading existing warning signs and adding new warning signs where appropriate.
• Installing a Rectangular Rapid Flashing Beacon (RRFB) at the pedestrian crossing on SR-35 just north of the intersection to improve pedestrian visibility.

Additional Improvements Along SR-84 in Woodside

Caltrans is also coordinating with the Town of Woodside on additional safety improvements along SR-84, including:

• Reducing the speed limit near Woodside Elementary School to 15 mph.
• Installing "SCHOOL ZONE AHEAD" warning signs.
• Supporting the Town's installation of two additional school speed limit signs.
• Reducing the speed limit near Woodside High School to 35 mph by November 2026.

Looking Ahead

Caltrans continues to evaluate additional opportunities to improve safety along the corridor.

Potential future traffic calming measures include speed feedback signs and other engineering improvements. Additional strategies, such as increased enforcement, automated speed enforcement where authorized, and speed limit changes, require coordination with partner agencies and local jurisdictions.

Caltrans will continue working with the California Highway Patrol, the Town of Woodside, San Mateo County, elected officials and other partners to identify and implement appropriate safety solutions.

Community Engagement

Caltrans recognizes the community's interest in improving safety along State Routes 9, 35 and 84.

Caltrans will continue coordinating with elected officials, local jurisdictions and partner agencies to hold a community meeting that will:

• Provide updates on ongoing safety improvements.
• Share implementation schedules and project progress.
• Answer questions from community members.
• Gather public feedback to help inform future safety strategies.

Additional information, including meeting details and project updates, will be posted to this page as it becomes available.

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Traffic Advisories

• September 29, 2026
  Striping Work at Intersection of State Route 35 and 84 for Four Corners Safety Improvements | Caltrans

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Project Contact

Nawel Tahraoui
Public Information Officer - Caltrans District 4
Nawel.Tahraoui@dot.ca.gov
(510) 390-3253

Page last updated September 2026