24 May 2015

Going the Extra Inch

Assisted level boarding on
Amtrak's Northeast Corridor
To enable wheelchair users to board a train without assistance, the Americans with Disabilities Act (ADA) requires level boarding platforms to have a maximum 3-inch horizontal gap with the train floor, and a maximum height mismatch of 5/8 inch (see 49 CFR 38.93).  When this specification is met, wheelchair users can safely and quickly board a train by simply rolling across the narrow gap between the platform and the train, giving it no more thought than when using an elevator.

Today, few commuter rail systems in the United States offer this level of accessibility.  The NCTD Sprinter (see video) may be the only one, and is often classified as "light" rail.  U.S. systems with level boarding (such as in the Northeast) have a gap of six inches or more between the platform and the train, requiring the use of bridge plates for a wheelchair user to board.  As shown in the photo above, train crew members must assist with the process of deploying the bridge plate, monitoring the wheelchair, and re-stowing the bridge plate.  Assisted boarding can easily extend station dwell times and cause delays, even on a rail system with level boarding.  These delays are allowed for by padding the time between successive trains, to prevent a delay from cascading to multiple trains.

So, just build the platforms close enough to the tracks and we're done, right?  It's not quite that easy.

Dynamic Vehicle Envelope

Dynamic envelope as defined
for Caltrain electrification
When trains are moving at speed, they can sway from side to side.  Suspension failures or shifting loads could even cause them to sag or lean to one side, requiring additional clearance between the track and nearby obstacles.  Station platforms form one such obstacle.  Caltrain's electrification RFP defines a dynamic vehicle envelope (shown at left, from page 95 of this PDF document) that encompasses the range of motion that can be expected from Caltrain's existing diesel fleet, future high-speed trains, and freight trains that use the peninsula corridor.  The dimensions of the dynamic envelope constrain how far from the track center line any future level boarding platforms would have to be set back, in order to prevent what is known as a "platform strike" from a train passing at speed.
  • 8" platforms (existing) are 64" from track center
  • 25" platforms would have to be 67" from track center
  • 30" platforms would have to be 68" from track center
  • 50" platforms would have to be 70" from track center
Meeting the ADA Gap

Unassisted level boarding in Zurich
(Siemens photo)

The vehicle envelope, because it is dynamic, forces a clearance between platforms and trains that is wider than the 3-inch ADA maximum for unassisted boarding.  To provide unassisted boarding without bridge plates, the gap can be bridged automatically by a moving step that extends from the train, a moment before the door opens.  As shown in the photo at right, this step is the key to ADA-compliant unassisted boarding for wheelchair users, and provides a more comfortable boarding interface for bicycles, strollers, luggage, and anything else with wheels.  The step retracts after the doors close, a moment before the train departs.

These gap-filling steps are quite common outside the confines of U.S. commuter rail, and all major vehicle manufacturers worldwide can provide them if the customer asks.  Video examples:
Another common and useful train feature is an automatically leveling suspension, to control the plus or minus 5/8" vertical alignment between the train floor and the platform regardless of passenger load or wheel wear.  A nice bonus of such a system is that it can measure passenger loads in real time.  This too can be provided by vehicle manufacturers if the customer asks.

Caltrain's Approach: What Gap?

Caltrain is now taking a "not to preclude" approach to level boarding, attempting to future-proof the new EMU fleet for any future decision regarding level boarding, pending the outcome of additional planning for the Caltrain / high-speed rail blended system.  This approach is largely a result of not having seriously thought about or planned for level boarding until quite recently.

[Update 6/14/2015: turns out that Caltrain's EMU RFP does require the ADA gap specs for unassisted level boarding!  My source had it wrong.]
As it turns out, Caltrain has no intention to comply with the ADA gap requirement.  Never mind the gap.  As will be apparent in the upcoming vehicle RFP, the new EMU fleet will comply with the ADA using crew-assisted boarding with bridge plates, even after level boarding platforms are built and regardless of the selected platform height.

If Caltrain fails to specify gap-filling steps and leveling suspensions for their new EMU fleet, then wheelchair users will still need crew assistance to board or alight, resulting in random and unpredictable impacts on station dwell times.  Such a failure would preclude reliable and punctual operation of the blended system, increase the amount of timetable padding between trains, and limit the capacity that can be extracted from the peninsula rail corridor before expensive and controversial infrastructure upgrades become unavoidable.  Gap-filling steps and leveling suspensions are perfect examples of small off-the-shelf features that pay off in the long run.

In order "not to preclude" an efficient blended system that extracts the highest capacity from limited infrastructure, Caltrain should require that the new EMU fleet be equipped for ADA-compliant unassisted wheelchair boarding, once new level boarding platforms become available.  Because the new fleet will be in service until the year 2050, this capability cannot be an afterthought and must be engineered into the new trains from the outset.


  1. The workshop presented by Caltrain was informative and interesting. Looks like they are exploring several options although one wonders why they are even considering doors with “traps.” Apparently the issue with the gap and high platforms has to do with pre-historic CPUC and FRA regulations; two agencies that have not gotten out of the 19th century, or is it the 18th century...??? Well we need a clear path for all those guys riding on the ladder on the outside of rail-cars.

    They say they want proven design/technology, isn’t the retractable step a proven design?

    Why should HSR dictate to Caltrain (and Metrolink), that 50” platform is the standard? HSR is also citing “proven” design at 50” and not considering anything in development at 25”. HSR also said that this is an improvement for all of California passenger rail.

    How will 50” or 25” be compatible with freight?

    How will 50” or 25” be compatible with conventional rail, ACE, Amtrak, Capital Corridor, heritage/steam excursion trips?

    Caltrain needs level boarding ASAP, how do we accomplish this on an operating system with as little disruption as possible?

    The capacity affected by additional doors, ADA space, bike space, or bathrooms can be addressed by longer and more frequent trains.

    Why only 6-car trains?

    Platforms can be extended, or doors stay closed where the platform is too short.

    Why only 6 trains per hour in each direction?

    Think outside the box, Caltrain could be handling over 125,000+ customers a day, if they run the proper service.

    1. Unless I'm mistaken, higher platforms would be compatible with freight because the planned loading gauge for HSR and Caltrain would be wider than that of freight.

      ACE, Amtrak, and Capitol Corridor would not need to be compatible with high platforms, because they only stop at Santa Clara and Diridon, and would have their own platform tracks at those stations.

    2. The trap design is not favored and may not even be in the RFP.

      They know they will need a waiver of CPUC GO 26-D (a rule that essentially forbids level boarding where freight trains operate-- unless you deploy expensive and maintenance-intensive measures such as retractable platforms, like NCTD, or gauntlet tracks, like SMART). They would do well to plan for a generous platform setback: every inch further from the track is one less inch they will have to haggle over with the likes of UPRR. 70 to 72 inches from track center isn't a crazy range to shoot for, giving freight trains all the side clearance they need. The Northeast makes do with 67 inches (see video) without the universe imploding.

      As for HSR at 50" floor height, it's their way or the highway. That doesn't sit well with a lot of people. Caltrain advocates disagree on which way to go. I say the HSR way at 50" is better than the highway (i.e. no shared stations). This approach won't be reverse-compatible with "conventional" passenger rolling stock, but that's okay since the amount of "conventional" traffic (even with planned future increases) will be just a side show to the Caltrain / HSR traffic. Some people won't get their wish of a modern-day Coast Daylight, and they'll just need to let go of that nostalgic vision.

      Caltrain can position itself to double or triple capacity if they make the right strategic moves now. Electrification is only the first step. Level boarding is the next. Then comes more grade separation at strategic locations. Then extra tracks as traffic warrants, but only as a last resort after every last drop has been squeezed out of the existing infrastructure. There's a lot left to squeeze, if the right moves are made.

    3. As you point out, all this should have been resolved years ago. It's hard to blame even the CPUC if no one approaches them with a request to update the rules. If it (appears to) work(s) don't fix it. It's also vital to involve Southern CA as quickly as possible. We have to design a blended system that is standard at both ends. Kind of obvious but too many Nortenos don't seem to be thinking about that.
      FWIW I've been telling Coast Daylight advocates to forget SF, unless you keep a dedicated low level track at the existing Caltrain station. You could then run expresses from Gilroy via San Jose with existing stock. But as far as the "Daylight" is concerned the construction period will be a nightmare. Best to go to Sac, or better yet Reno.

  2. While the Cascade Talgos are not level boarding by any means, they have automatic, retractable steps that open with the doors, right here in the USA

  3. What freight is there north of Redwood City?

    1. Gravel to the spur out to the Port of Redwood City.
      The occasional noisy freights run through San Carlos, after 10pm, hauled by rusting-out GPs that still have Rio Grande and SP livery. I've heard flat wheels making horrible sounds, weekend daytime, outside Hillsdale mall.

    2. Aggregates go to Graniterock Road Materials at 1321 Lowrie Ave, SSF. There must be other customers up on the north end because a variety of other cars/loads can often be seen parked in the SSF yard.

    3. Don't forget the mighty Port of San Francisco

  4. Does it cost UPRR more than it's worth to maintain the freight infrastructure north of Redwood City?

    1. Do you seriously think someone here has access to UP's books!?

    2. What is UPRR required to do in order to keep the infrastructure up to snuff?

    3. Umm, fix stuff that isn't Caltrain's. Where is this dribble of dumb questions going?