Overview

• Caltrans opened the new three‑lane configuration on Monday between Novato and Petaluma, marking a major Marin‑Sonoma Narrows milestone after years of work.
• The $762 million project now provides a roughly 50‑mile contiguous carpool corridor from the Richardson Bay Bridge to Windsor.
• Weekday HOV hours in Marin and Sonoma shifted on Sept. 8 to 5–10 a.m. and 3–7 p.m. in both directions to match regional policy.
• Commuters and some local officials report longer trips and new bottlenecks, and a Change.org petition opposing the expanded hours has drawn nearly 5,000 signatures.
• Caltrans and partner agencies plan to study post‑opening traffic before any adjustments, which they say would take months, while overnight work and ramp closures continue this week near San Antonio Road.