Original Post: When we reviewed just how wide the Caltrain corridor is, we assumed a 75-foot minimum width for a four-track rail corridor, measuring from fence to fence. New figures, obtained from reliable sources, indicate typical dimensions will be quite a bit more:
- 15' (4.6 m) Caltrain track spacing (measured center-to-center)
- 16'6" (5 m) HSR track spacing, or between HSR and Caltrain tracks
- The kicker: 23'6" to 28'6" between the outer track center line and the boundary fence, to allow for third-party utility easements (as already exist in many places along the Caltrain corridor), overhead electrification poles, maintenance walkways, drainage structures, etc.
Time to Panic?
Well, maybe not quite yet.
These figures are quite likely quoted for the nominal situation, where plenty of land is available. Indeed, more than two-thirds of the peninsula rail corridor is 100 feet or wider, allowing generous side clearances. Caltrain's own environmental documents, drafted for the electrification project long before HSR came along, include the typical four-track section reproduced at right, with a nominal fence-to-fence width of 89 feet.
Then again, the HSR numbers are incredibly generous by international standards, and probably accommodate vehicular access along both sides of the right of way. (A Department of Homeland Security Crown Victoria is 6'6" wide, for reference.)
The minimum legal side clearances in California are dictated in CPUC General Order 26-D. The absolute minima are 14' between track centers and 10' side clearances to the edge of the right-of-way. Caltrain's engineering standards reflect these constraints in a clearance drawing. None of these standards envision trains running at 125 mph and above, since those have never existed in California. Better numbers can be gleaned from foreign standards, for example the German Eisenbahn, Bau- und Betriebsordnung (EBO). That particular standard requires the following side clearances:
- A danger zone (free of any obstructions such as poles, walls, etc.) of 2.5 m (8'2"), measured from the track center line, for train speeds less than 160 km/h (100 mph) and 3.0 m (10') for greater speeds.
- Outside of the danger zone, a 0.8 m (2'6") space for rail personnel to take refuge at a safe distance from trains
- The danger zones of neighboring tracks may overlap, with tracks spaced 4 m (13') for speeds less than 250 km/h (150 mph) and 4.2 m to 4.5 m (14' to 15') above. Since European trains are about a foot narrower than ours, that's roughly consistent with the 15-foot minimum already in use on the peninsula.
If one had to make an educated guess about the minimum allowable corridor width, as opposed to the typical width, it would likely be closer to the values in the German EBO and/or the European Technical Specifications for Interoperability (TSI). Using the 16'6" track spacing mentioned above, that comes out to 0.8 m + 3 m + 5 m + 5 m + 5 m + 3 m + 0.8 m = 22.6 m, or 75 feet. The actual minimum for the peninsula corridor is likely to be spelled out in the upcoming draft Analysis of Alternatives.
Those figures are only valid for an alignment at grade level, which is the narrowest option. Raising or lowering the tracks requires additional width for construction.