If we assume the next several decades will be like the last several decades, we can take an educated guess about how and in what order grade separations will be built. The criteria for prioritizing each project could be:
- creating long, uninterrupted stretches of grade separated right of way to enable higher train speeds without compromising safety
- creating a four-track mid-line overtake facility to increase the capacity of the corridor, to support initial HSR service
- separating crossings that rank highest in the CPUC's Section 190 Grade Separation Priority List
- delaying the most expensive and politically costly projects until last
|Phase I: San Bruno Grade Separation
Phase II consists of four projects in San Mateo County, opening up two long stretches free of crossings by the early 2020s, including 14.8 miles free of crossings north of Burlingame, and 6.5 miles south of San Mateo. This enables the future construction of the "short" mid-line overtake envisioned in Caltrain's corridor capacity analysis, and leaves only a few dense clusters of crossings within San Mateo County. The new grade separations, in order of priority, are:
- 25th Ave in San Mateo, the only grade crossing that remains between San Mateo and Redwood City. Along with new grade separations already planned at 28th and 31st, this project enables the future 4-track mid-line overtake.
- Broadway in Burlingame, an extremely congested crossing that has been slated for grade separation since the 1970s. It rates #11 statewide on the latest CPUC priority list.
- Linden Ave in South San Francisco, originally planned as part of the San Bruno project, but dropped from the final design in 2007. Grade-separation at Linden is accompanied by the closure of Scott St, which becomes a pedestrian tunnel.
- Center Street in Millbrae, a grade separation that will require a U-shaped elevated ramp due to the nearby BART subway tunnel box. Such are the consequences of bad planning.
|Phase II: San Mateo County Grade Separations
- Mary Ave in Sunnyvale, the corridor's busiest grade crossing in this county, with more than 25,000 daily vehicles
- Sunnyvale Ave
- Rengstorff in Mountain View, with about 18,000 daily vehicles
- Castro in Mountain View, with about 9,000 daily vehicles
- Charleston and East Meadow in Palo Alto, with a combined ~30,000 daily vehicles plus numerous pedestrians and bicyclists
- 16th and Common in San Francisco, as part of the DTX project
|Phase III: Santa Clara County Grade Separations
Phase V is the Great San Mateo / Burlingame Grade Separation. This is a tougher project because it involves some of the most highly constricted portions of the corridor. It also involves political and technical coordination between two neighboring cities, adding an additional challenge. The sheer quantity of crossings (13 grade crossings + 4 obsolete grade separations within 2.4 miles) is also a complicating factor.
Phase VI is the Great PAMPA Grade Separation. This project is left for last because it lies in the most expensive real estate on the corridor, involves coordination between three different cities, and is liable to cause the fiercest political and legal backlash anywhere on the peninsula. Delaying it until last, perhaps into the late 2030s, allows the customarily long planning process to run its course without undue haste in all three affected communities.
We didn't arrive at today's state of grade separation (more than half) overnight. It resulted from a slow and steady process that began in earnest in the 1940s. The future is likely to be similar, and the peninsula rail corridor can reach a far improved state by separating just 12 more crossings over the next couple of decades, as described in Phases II and III. This dozen should be prioritized for construction, before any of the crossings in the remaining dense clusters are touched.