Quick Links (discussed extensively below)
- San Bruno Done Right dimensioned plan view PDF (224kb)
- San Bruno Done Right 3D model (1.1mb) for Google Earth
Caltrain's design for the San Bruno station was conceived for commuter rail operations, with two extra tracks added ostensibly for HSR but equally useful for Baby Bullet express service. Whatever they may claim, Caltrain's old design is not compatible with high speed rail and threatens to lock in two disastrous design decisions before the conceptual engineering for HSR is complete.
First, the exceedingly sharp 60 mph curve at San Bruno would delay each HSR service by about 40 seconds; this curve was previously singled out as the worst curve for HSR on the peninsula corridor. This curve is so sharp that it needs flange greasers (shown at left) to squirt lubricant on train wheels, to mitigate wear and noise. Nevertheless, Caltrain officials have expressed ambivalence about straightening San Bruno curve, believing that the few seconds it would save are insignificant. A few seconds here, a few seconds there, and pretty soon it ain't high speed rail anymore... But why should they care, indeed? Straightening the curve for 100+ mph provides zero operational benefit to Caltrain. Any why would the CHSRA care, as they are tripping all over themselves to get something--anything--funded, and shovels turning dirt? Unfortunately, jerking a high speed train through a sharp 60 mph curve is very energy intensive and environmentally wasteful, and fundamentally at odds with modern train control software which seeks to minimize energy consumption. Assuming a realistic, environmentally appropriate, energy conservative speed profile, the San Bruno curve threatens to cost HSR far more than the 40 seconds lost in a lead-foot acceleration scenario.
Second, Caltrain's new station design at San Bruno puts the platforms on the outside, with the express tracks in the center. As was discussed in Slow Traffic Keep Left, this is probably not the best arrangement for a corridor shared with HSR, mainly because Caltrain service disruptions can propagate to HSR and disrupt service state-wide. Where to put the express tracks, and thus where to place Caltrain station platforms, is one of the most fundamental design decisions to be made on the peninsula, and it should be decided by a rigorous trade study. Such a momentous, corridor-wide decision should not default to five-year-old plans drawn up outside the high speed rail project.
San Bruno Done Right
Since a picture is worth a thousand words, a 3D model may be worth a thousand pictures. Here is the future San Bruno station and grade separation done right: with the curve straightened out for 100 mph operation, and a central island platform for Caltrain.
Download Google Earth model, enable the Terrain checkbox, and click on Tour. Make sure to fully explore the details of the station area, including stairways and platform canopy. (The necessary viewer, Google Earth, is free and easy to install.) At the new San Bruno,
- All pedestrian access paths lead to the correct platform.
- High speed trains, running on the outside tracks furthest away from the platform, save at least 40 seconds by avoiding the need to slow down for the sharp curve. That doesn't sound like much, but it's nearly half a percent of the entire express run from San Francisco to Los Angeles. Savings like this are too good to pass up.
- A continuous viaduct can be built across both San Bruno and San Mateo avenues, resulting in easy pedestrian access from anywhere in the vicinity of the station.
- The changes affect only the station area and adjacent curve. The remaining grade separations are identical to those proposed by Caltrain.
For the track geometry junkies out there:
- The vertical track profile is similar to Caltrain's (see Appendix B page 4).
- The new horizontal alignment (see dimensioned plan view PDF) features a 1200 m (3900 ft) radius curve, good for 109 mph at 12 inch total equivalent cant or 100 mph at 10 inches.
- The 210 m (700 ft) long by 9 m (30 ft) wide platform is very slightly tapered to minimize the area consumed by track slews at each end of the platform; the radius of the southbound platform face is 6000 m (20,000 ft) and produces a less than 1 cm (3/8 inch) ADA-friendly platform gap, with a benign, ADA-friendly 25 mm (1 inch) superelevation, as demonstrated by the Bombardier cars placed in the 3D model.
- It is likely that all four tracks can fit under the I-380 viaduct without moving any support columns. Even if this were not feasible, and supposing that it became necessary to relocate one row of six columns, the CHSRA has already demonstrated a willingness to move freeway supports in their design for the north end of Tunnel #2 under I-280 in San Francisco. If it makes sense there, it makes far more sense in San Bruno.
- In recognition of the tight clearances under I-380, accurate Bloss spiral transition curves are shown. The tracks and station foundations do not interfere with existing BART tunnel, and the curve is configured so as to fit between the I-380 support columns while minimizing excursions from the existing right of way boundaries. These improvements are likely feasible without major re-engineering of adjacent civil structures.
Many thanks to Richard Mlynarik for his 3D modeling skills and advice on track geometry.