Mill Valley Congestion Improvements and Traffic Signal Timing Project

At the March 5th City Council Meeting Public Works Director Andrew Poster presented a summary of the improvements gained from the recent traffic signal synchronization project and outlined upcoming efforts to tackle congestion in Mill Valley. The recently completed signal synchronization has significantly improved weekend traffic flow through the Camino Alto-East Blithedale intersection and have made moderate improvements during weekdays. In addition to the synchronization project the City is working with regional partners including Caltrans and the Towns of Tiburon and Belvedere to tackle congestion problems near the Blithedale Avenue/US 101/Tiburon Boulevard (SR 131) interchange.

The Traffic and Congestion Reduction Advisory Task Force led by then Mayor Ken Wachtel, made more than four dozen short-term and long-term project recommendations to relieve traffic congestion and improve travel time on our main corridors: Blithedale and Miller Avenue including an annual review of and adjustment to signal timing. The short-term projects that are within the City's control have been implemented while long-term steps typically require significant funding and partnering with other local and state agencies. 

The Traffic Signal Timing Project was implemented May 22-26, 2017 and a second round of observations was completed four months later in September, after schools returned from the summer break, and a few final adjustments were made. After implementation of the timing updates and follow-up adjustments, travel times were measured by Kimley-Horn in May 2017 along East Blithedale Avenue-Tiburon Boulevard between Camino Alto and the Redwood Frontage Highway, during both the weekday and weekend conditions. The travel times study showed an average decrease in travel time following implementation of the timing improvements of approximately 6% percent on weekdays and 30% on weekends, between January 2017 (pre-installation) and May 2017 (post installation). Although there was an observed decrease in travel times on both weekdays and weekends with the timing adjustments, there remains significant congestion along the corridor during peak periods.

Working with the Caltrans Signal Division, the signal timing of the US 101 south-bound off ramp at the west end of the overpass was reprogrammed to match the coordinated programs of the Mill Valley signals at Lomita/Roque Moraes and Tower/Kipling resulting in a small improvement to traffic flow approaching the freeway. 

We also made a significant change in the signal function at the Camino Alto-Sycamore Avenue intersection to address chronically long signal times by setting that signal to run in "Free" or non-coordinated mode.

The large volume of traffic on the Mill Valley streets remains the single largest factor in traffic congestion and overall service at each signal. Additional traffic congestion relief will require infrastructure improvements beyond the improvements that could likely be gained through implementation of annual signal timing adjustments. To that end, the City of Mill Valley is working with regional partners to tackle larger infrastructure changes at our bottleneck the Highway 101 interchange.


Future Improvement Projects

Although not included as part of this traffic signal timing project, staff is currently working with other agencies to improve the Blithedale Avenue/US 101/Tiburon Boulevard (SR 131) interchange. A northbound 101 On-Ramp widening project is currently being designed by Caltrans and is expected to improve traffic congestion along Blithedale Avenue in Mill Valley. This project is currently anticipated to be completed in 2020. As it is unlikely that there will be a significant reduction in traffic volumes, continuing to look for creative solutions to improve the geometric limitations of East Blithedale Avenue, the 101 overpass and the Redwood Highway Frontage is likely our course of action for reducing traffic congestion.

Click here to watch the presentation to City Council