City of Mill Valley Traffic Update: What’s Driving Traffic Congestion and Our Efforts to Solve the Problem

Throughout the summer, the City of Mill Valley has adjusted the timing of the six traffic lights it controls from the Camino Alto and Miller Avenue intersection out to East Blithedale Avenue, Tiburon Boulevard and Highway 101. Traffic flow has improved, but peak period conditions remain unacceptable.

Director of Public Works Jill Barnes has worked with Caltrans and requested further synchronization  of the three traffic lights Caltrans operates on East Blithedale Avenue/Tiburon Boulevard at Tower/Kipling drives, at the southbound on-ramp of Highway 101 and at the Highway 101 northbound on-ramp to alleviate the bottleneck they create during peak traffic conditions. Caltrans engineers have agreed to make additional adjustments to these signals as the City has requested.

Primary Cause of Congestion

Ms. Barnes has also determined that a dominant cause of the recently increased traffic congestion is a shift in vehicle volume onto Camino Alto and East Blithedale as residents attempt to avoid the congestion through Tam Junction related to the traffic lights installed there in October 2013. A May 2014 update from Supervisor Kate Sears summarized efforts made by the County of Marin and Caltrans engineers to reduce delays and congestion caused by the new signals at Tennessee Valley Road and Flamingo Road (click here for the summary). The July 7 staff report to the City Council provides the City’s findings regarding traffic conditions and recommendations for improvement.

“In addition to the lack of optimal signal coordination on East Blithedale and the 101 overpass, we have determined that the new Caltrans signal at Tennessee Valley Road/Shoreline Highway is the dominant contributor to the increased traffic volumes and resulting congestion we have regularly experienced on our roadways and the subsequent traffic congestion and substantial motorist delays,” City Manager Jim McCann wrote in a June 11 letter to the District 4 Director of Caltrans, requesting an immediate meeting to develop a plan to resolve these issues.

Representatives from Caltrans, the County of Marin Public Works Department and the Transportation Authority of Marin have met with City of Mill Valley officials three times in recent weeks to discuss the situation and cooperatively identify solutions to the traffic issues.

The City has conducted traffic counts for seven days on East Blithedale Avenue between Lomita Drive and Tower Drive/Kipling Drive, as well as counts of cars turning off east Blithedale/Tiburon Blvd. onto northbound and southbound Hwy. 101 and on Miller Avenue west of Almonte Blvd. and on Camino Alto at both Miller and East Blithedale avenues. Traffic data was collected during morning, mid-day and afternoon/evening peak periods.

We agree that the changes to the signal will improve circulation to the intersection, but we believe further modification is necessary. The City is pursuing additional changes with Caltrans leadership.

“The traffic count data confirms our observations that we have had about a 15 percent increase in traffic volume on East Blithedale just since last November,” Public Works Director Jill Barnes said.

That 15 percent jump reflects a spike in traffic volume as a result of the installation of new traffic lights by Caltrans and the County of Marin along Shoreline Highway at Tennessee Valley Road and Flamingo Road. The increase is simply more than Mill Valley’s road can handle, regardless of the timing of its traffic lights, Ms. Barnes said.

Efforts to Reverse Traffic Shift and Improve Circulation

The traffic signal timing changes the City made in early May were designed to increase the green light times for drivers along Camino Alto and East Blithedale, helping move traffic along those corridors more quickly, and also to provide required “Walk” times for pedestrians, Ms. Barnes said. But the timing was based on historically normal traffic volumes on these streets that existed before the Shoreline Highway signals were added.

“The refined signal timing does in fact work to improve the efficiency of our roadways and move traffic more quickly,” Barnes said. However, our major roadways are at capacity and the diversion of such a substantial volume of traffic from Shoreline Highway to Camino Alto and East Blithedale has overwhelmed these roads and has brought traffic to a standstill on numerous occasions.

For City of Mill Valley officials, reducing traffic backups is a major priority. The City will continue to insist to Caltrans and County engineers that the Tennessee Valley Road signal be modified to allow Shoreline Highway to function efficiently for vehicles and to reverse the shifting of traffic we have experienced in recent months. We will also continue to work with Caltrans to make further signal timing adjustments to improve synchronization and on-ramp modifications to improve overall roadway efficiency.

“We recognize the need for safety measures to allow pedestrians to cross at the new Tennessee Valley Road/Shoreline Highway signal,” City Manager Jim McCann said. “We simply want the signal modified to correct the significant decrease in the functioning of the intersection, which has caused delay and great frustration to motorists and has resulted in the shift of traffic into Mill Valley and onto the already over-burdened Camino Alto and East Blithedale Avenue. We need the cooperation of our County and Caltrans colleagues to make these modifications to benefit all users.

Caltrans and the County agreed last week to make modifications to the signal which will reduce traffic delays along this corridor; these modifications should be in place by August 22.

An update of the City’s efforts and the actions of the County and Caltrans will be provided to the City Council at its September 2 meeting.

Correspondence with Caltrans :

Letter to Caltrans –
June 11, 2014

Caltrans Reply –
July, 8, 2014

Letter to Caltrans –
August 12, 2014


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