The effect is to free California from the prescribed platform interface in use on the Northeast Corridor, where the platform edges are located 48 inches above the top of the rail and offset laterally by 67 inches from the center line of the track. An earlier recommendation that Caltrain should use high platforms to ensure compatibility with high-speed rail, especially in highly constrained stations like San Francisco Transbay, still stands. The specific dimensions of the platform interface, however, can be optimized for California at a height less than 48 inches and offset greater than 67 inches.
Let us briefly review the Unique Local Conditions present in California:
- "blended" commuter / HSR service
- bi-level commuter rolling stock, both in the north (Caltrain) and south (Metrolink)
- single-level HSR rolling stock, at the CHSRA consultant's insistence
- a strict requirement for level boarding, per Americans with Disabilities Act, unlike Europe
- no pre-existing level boarding standard, unlike Amtrak's NEC
- a very tall (17 feet, AAR Plate F) loading gauge, unlike Amtrak's NEC
Future trends in high-speed train design
|Stadler EC 250, with a 760 mm floor|
Not too high, not too low, just right
760 mm is a good compromise platform height because it satisfies two conflicting requirements:
- it is low enough that a Caltrain or Metrolink double-deck EMU could be designed with entry doors on the lower floor without making the train excessively tall, and
- it is high enough that a single-deck high-speed train can be designed with a continuously accessible floor with no interior steps throughout the entire length of the train, per ADA requirements.
Floor heights higher than 760 mm are not practical for boarding and alighting from the lower level of a bi-level EMU, and push the entry doors out over the wheels at the ends of train cars, resulting in unevenly-spaced doors that may impede passenger flows on station platforms and increase station dwell times.
Stepping up to 760 mm (30 inches)
The transition to level boarding, regardless of the selected platform height, will not take place overnight. For logistical and financial reasons, there will be a period of several years during which commuter trains will serve a mish-mash of old and new platforms at differing heights. To allow uninterrupted service through this transition, the trains will require built-in movable steps to serve both heights.
This isn't a new problem. Numerous trains worldwide have been designed to address it, as seen in the image and videos below.
YouTube videos of moving steps:
Paris, France (step action at 0:30)
Zurich, Switzerland (step action at 1:25)
San Fancisco MUNI
Vienna, Austria (gap filler only)
Stuttgart, Germany (gap filler only)
Leipzig, Germany (gap filler only)
|Step deployed for a low platform on a Paris|
commuter train. Photo credit: Poudou99
The lesson is clear: these mechanisms must be designed with the utmost simplicity and reliability. For Caltrain's new EMU fleet, that could be nothing fancier than a single step deploying from each door, as shown in the cross-section diagrams below. Train floors are drawn in dark red.
The EMU steps, shown in the third diagram from the top, are a bit taller than one would like with an 11-inch rise. That's 1 inch taller than today's first step, but probably acceptable for a temporary transition period until all platforms are raised and the step mechanisms can be permanently retired.
Note also that as drawn here, the extra width of the new cars would place the new platform edge 70 inches from the track center line, a full six inches outside of the nominal Plate F loading gauge. This dimension might ease any concerns from Union Pacific that high platforms would interfere with freight service, or from the government about STRACNET clearances.
This is a compromise solution, and as such it isn't ideal under every criterion:
- the floor height is a bit higher than one would like for a bilevel EMU
- the floor height is a bit lower than one would like for a single deck high-speed train
- there is a failure-prone moving step mechanism
- the step height is awkwardly tall
Gradual Transition Strategy
Getting from today's 8-inch platforms to 100% level boarding isn't something that requires a mega-project right after (or worse, during) electrification. It can be done piecemeal, on a station-by-station basis as funding becomes available for each, exactly like the 37 platforms built in the last 15 years. The timeline can expand or contract to match any budget. Here's the simplest way to get from here to level boarding:
Thinking about this transition ahead of time, and designing the EMU fleet around the new platform interface, has essentially zero up-front cost. In the long run, doing it right the first time saves money because we won't have to do it over in order to achieve the numerous benefits of level boarding.
Caltrain may not fully realize this, but their decision about the platform interface for their upcoming EMU procurement could set a generational precedent for the entire California rail system. Will they give it the consideration it deserves?