SamTrans Dumbarton Corridor Study – the hidden highway

The complex, multi-modal package of proposed transportation investments in the SamTrans Dumbarton Corridor Transportation Study includes a major program to improve transportation for solo drivers, including “freeway-izing” Highway 84/Bayfront Expressway. The hidden highway project may come as a surprise to those who have heard SamTrans’ presentations, which describe the project as primarily about improving transit use.

The “hidden highway” will come as no surprise to community members who have been listening to the conversations about Menlo Park’s General Plan. In those conversations, several city council members and planning commissioners have been advocating strongly for moving forward with proposals to convert “Bayfront Expressway”, the large arterial which moves Westbound drivers from the bridge out to 101 at Marsh Road, into a full freeway by adding interchanges that bypass stoplights at the major through cross-streets of University, Willow, and Marsh.

Proponents of freeway-izing 84 make the case that it will alleviate congestion for commuters, and relieve cut-through traffic from neighborhoods in East Palo Alto and East Menlo Park, because drivers will be able to speed out to 101, instead of being tempted to cut-through on University or Willow.

The freeway concepts are taken from the ten-year-old “Peninsula Gateway Corridor 2020” report. That study focused on relieving Dumbarton corridor congestion, looking only at roadway changes to achieve the goal, not at transit and transportation demand management options.

The Peninsula 2020 report was done when the area at the base of the bridge was a car-centric single-use business park, before Facebook moved into the buildings built by Sun at the base of the Dumbarton bridge, and was required to maintain parking for 50% or fewer employees; and before cities including Palo Alto, Mountain View, Menlo Park and Redwood City had adopted policies to reduce solo driving. The report was done before Menlo Park updated its General Plan with plans to evolve the area into “live-work-play” neighborhoods with housing and services near jobs, designed to be walkable, bikeable, and have pleasant public spaces.

There are a number of reasons to be concerned that the program to “freeway-ize” 84 may not have the desired outcomes to relieve congestion and cut-through traffic, and improve quality of life for residents in Belle Haven and East Palo Alto. This blog post highlights the “hidden highway” project, and raises questions to help assess whether that project component will achieve the goals of its proponents.

The Hidden Highway

This map shows the package of highway components. The program includes express lanes on 84 to enable buses, carpools, and toll-paying solo drivers to move faster across the bridge.


Other highway components:

  • Add a flyover in East Palo Alto to speed drivers up University, or past University on 84
  • Add an overpass or underpass at Willow, across from the location that Facebook plans to add housing, a grocery store, and public space
  • Add a hairpin turn at Marsh for drivers on express lanes to travel directly onto 101 express lanes

Will it relieve congestion and cut-through traffic?

The crucial question is whether these projects will achieve the transportation goals that proponents hope for, and whether they are the best solutions to achieve these goals, given current conditions. There are a number of questions:

Will the express lanes actually improve end to end travel time? Data in the report suggests that nearly 40% of drivers crossing the bridge are heading to destinations in Palo Alto and Menlo Park. To reach these destinations, drivers will need to traverse the already clogged sections of Willow or University toward the hills from 101. Would the changes move the bottleneck upstream? (These upstream sections are in well-off neighborhoods that have definitively rejected road widening to help commuters speed through their neighborhoods.)

Will speeding solo drivers increase driving? The report estimates that about 25% of drivers will use the express lanes, instead of taking local streets directly through East Palo Alto and Belle Haven. However, in Appendix G8, the report states that without the projects, by the year 2040, at the PM peak period, only 78.5% of demand will be served because of congestion. Does this imply that if the projects relieve the congestion, that an additional 21.5% of drivers will be attracted to the corridor – about another 25,000 cars at the time? If so, wouldn’t that cause the congestion to return, and worsen on the narrow upstream sections?

How will these interchanges affect the neighborhoods they are added to? The schematic diagrams in the report make it very difficult for lay-people to decipher how these new highway elements will look. A local transportation planner estimates that the Willow interchange may resemble this intersection of Maude and 237 in Sunnyvale. How will this infrastructure affect the appeal of the nearby housing, services, and public space that Facebook is proposing to build?  Residents in the area are asking for more detailed renderings to visualize the change to their neighborhood.


Is freeway-izing 84 the most cost-effective solution to relieve congestion and cut-through traffic? The three major components at University, Willow, and Marsh are estimated to cost $300,000,000, and to be added by 2025. In addition, toll revenue is expected to be $70,000,000 per year. If, instead of freeway-izing 84, the money were used for Stanford-quality TDM programs, the system could provide $250 per month benefits for transit passes, carpool services, guaranteed ride homes, first-mile assistance, and concierge services.

Rather than waiting until 2025, such programs could be be started in the next few years, become more effective as toll lanes are added. If they are successful, then there may be lower need for highway interchanges.