Tam Junction Traffic Light Update from Supervisor Kate Sears

County of Marin - Supervisor Sears

What’s the latest on the Tam Junction traffic lights?


Marin County Public Works and Caltrans are continuing to adjust the signal timing along Shoreline Highway to improve the flow of traffic. Caltrans maintains and operates the traffic signals including implementation of traffic signal timing for the corridor. Marin County is assisting in the review of traffic conditions along the corridor and has hired a traffic consultant to provide additional assistance to Caltrans.


The primary concerns residents have recently told us about are:


1) left turn from Shoreline Highway onto Tennessee Valley Road,

2) side street (Gibson Avenue) traffic at the Flamingo/Shoreline Highway intersection,

3) travel times in the afternoon from Tamalpais High School to US 101, and

4) pedestrians crossing Shoreline Highway at Tennessee Valley Road.


The County has reviewed each of these issues with Caltrans and measures to address them are discussed below.


Left Turn from Shoreline Highway onto Tennessee Valley Road


Residents wrote about long wait times to turn left from Shoreline Highway northbound onto Tennessee Valley Road. Caltrans adjusted the signal timing to increase the frequency of the green light allowing the left turn onto Tennessee Valley Road from Shoreline Highway northbound.  This change should reduce the wait times as well as the number of cars waiting in line to turn.  Caltrans implemented an initial change during the PM peak hours when the long wait times were observed. 


County staff will continue to monitor traffic conditions to assess the effect of the recent signal timing changes. Further signal timing adjustments during the PM peak hours and other times may be forthcoming.


Cars waiting to turn left from Shoreline Highway onto Tennessee Valley Road often extend past the existing left turn lane pocket. Based upon field measurements, extension of the left turn lane pocket by 40 feet (approximately 2 to 3 car lengths) appears to be feasible. County staff is coordinating with Caltrans to restripe and extend the left turn lane pocket at this location.


Flamingo Traffic Signal and Side Street Traffic


The County’s Department of Public Works has received complaints regarding how quickly and often the traffic from Gibson Avenue interrupts through traffic on Shoreline Highway. Caltrans will adjust the traffic signal program to ensure that a vehicle or pedestrian on Gibson Avenue is not immediately accommodated by the traffic signal; i.e. a short wait time at Gibson will be programmed at this light. DPW believes a longer wait time at Gibson Avenue will be workable and less disruptive to the through traffic on Shoreline.


Lengthy Travel Time in the Afternoon from Tamalpais High School to Highway 101


We have recently received complaints about lengthy travel times in the afternoon from Tamalpais High School to Highway 101. Long travel times had not been observed in the afternoon during previous travel time surveys.


Due to concerns over pedestrian safety, Caltrans recently made some changes to the pedestrian timings at Almonte and Shoreline.  These changes likely led to the recently observed travel time increase from Tam High.  Caltrans will consider adjusting the pedestrian signal settings back to the settings that were in place a few weeks ago, with the expectation of restoring flow.


The need to balance safe pedestrian, transit user and bicycle access with motorists’ desire for smooth traffic flow at the various lights throughout Tam Junction means that Caltrans has had to factor in a large number of variables in making signal adjustments. Depending on the time of day, those variables change and require careful light timing adjustments. Once a change is made, the resulting impacts need to be further studied and evaluated. We recognize the importance of making sure the movements of pedestrians, bicyclists, transit users and motorists are properly observed, analyzed, adjusted and tracked. Trying to get it right for all users is an iterative process which is complex, timing consuming and often frustrating for everyone.


Pedestrians Crossing Shoreline Highway at Tennessee Valley Road


A number of residents have raised concerns about motorists turning left onto Shoreline Highway from Tennessee Valley Road not expecting pedestrians to be crossing Shoreline Highway at the same time. Warning signs have been installed on the traffic signal poles to remind motorists to yield to pedestrians in the crosswalk. Caltrans has also adjusted the traffic signal timing to activate the green “walk light” five seconds prior to motorists on Tennessee Valley Road eastbound receiving their green light. This adjustment allows pedestrians to get a head start crossing Shoreline Highway and to be more visible to motorists. County staff is also coordinating with the W-Trans traffic consultant and Caltrans to examine other options available within State regulations at this location.


Caltrans obtained recent traffic counts for the intersections along Shoreline Highway. Caltrans staff will review these counts and may make additional traffic signal adjustments to better manage the traffic flow.


See Something? Say Something!


If you have further observations about the traffic lights in the Tam Junction area, please continue to send us your detailed description of the situation (list your chief concern with the date, time of day, path of travel and any suggestions).


What happens if I do say something?


We forward all your emails to our Department of Public Works for its consideration and analysis. DPW, in turn, shares this information with Caltrans traffic and signal engineers for their use in adjusting signal timing and identifying other solutions to help ease traffic flow.


Thanks to everyone for communicating your concerns and for helping us find a constructive approach to living with these new traffic lights. You, as residents, well know the traffic challenges Tam Junction presents – motorists, cyclists, students and adults traveling to school and work, pedestrians, hikers, visitors, and patrons of Tam Junction’s commercial businesses. Keeping everyone safe, keeping everyone moving, trying to reduce unnecessary traffic impacts to residential streets and prevent frustration sometimes can seem like a Sisyphean task, but we’re on it!


We’ll continue to send messages and updates as we receive helpful information to share. Please continue to send traffic related messages to my Aide, Maureen Parton at mparton@marincounty.org.


Reminder to Ride the Muir Woods Shuttle


And don’t forget to tell visiting family, friends and neighbors to take the Muir Woods Shuttle to Muir Woods and the parklands! Trip reduction and fewer vehicle miles traveled can be fun and community building. Plus, your traffic weary neighbors will thank you.


Here’s the link to this wonderful service, 9 years in successful operation:




Let’s all have a safe and enjoyable summer!