The Virtues of Width

The Swiss rail vehicle manufacturer Stadler was recently awarded a contract for 112 bilevel EMU cars to be delivered by 2016 for the Moscow airport express, based on their modular KISS vehicle concept.  A rendering is shown at right, complete with retro-Soviet hood ornament.  (UPDATE 6/2013: datasheet now available).  These EMUs are noteworthy because they take full advantage of the generous Russian loading gauge (the available height and width clearances), resulting in two spacious levels of passenger seating, and also because they use high platforms.  This is a European EMU on steroids, and Caltrain should take notice.

In a blended HSR + Caltrain system, slowly transitioning to full grade separation over a time scale of decades, several constraints exist that will impede Caltrain's ability to add capacity to meet increasing ridership demand:

• More trains per hour won't work.  Because there are only two shared tracks, the capacity of the corridor (as measured in trains per hour) is limited.  It's going to be a stretch for Caltrain to operate six trains per hour per direction with HSR in the mix, so adding more is clearly out of the question until the much-dreaded additional tracks are built.
   
• Longer trains won't work.  Train length is limited at stations such as Burlingame and Menlo Park, where grade crossings are found at both ends of the station platforms.  Until these locations are grade-separated and new longer platforms are built, adding more cars to make longer trains is not feasible.  In any case, most Caltrain platforms limit train lengths to 600 feet (or 7 standard-length cars), at least until they are rebuilt.
   
• Taller trains won't work.  Today's bi-level trains already take good advantage of the available height, so there is no seating capacity to be gained by growing trains any taller.

Loading gauge comparison,
Russia / USA / Europe

If more, longer, or taller trains can't satisfy increasing ridership, why not give wider trains a try?  The Russian 1-T loading gauge, shown at right in comparison to the loading gauges of western Europe and Caltrain, allows trains that are almost six inches wider than ours.  Going even a few inches wider than the Russian limit, with a 134-inch wide car shell, would enable five-abreast seating at the same level of comfort offered in Caltrain's existing Bombardier cars.

The Advantages of Extra-Wide EMUs

The diagram below shows a cross section of three double-deck trains: a traditional European EMU of the sort coveted by Caltrain; a Caltrain Baby Bullet car; and a hypothetical extra-wide EMU with comfortable five abreast seating, a few inches wider than the Russian model described above.

Such an extra-wide EMU has several advantages.

• More passengers per train.  With five abreast seating, 15 to 20% more seating can be provided without increasing train length or train frequency.  Even in those areas without seats, more floor space is available for standees.
   
• More usable space.  Extra width makes for more spacious and comfortable vestibules, stairs, and passageways between cars.  High-traffic areas near doors, bicycle racks, restrooms, and luggage racks do not impede the flow of passengers.
    
• Lower crew costs.  The number of conductors required on a train is dependent on the number of cars in the train.  Under the present labor agreement, there is a strong incentive to keep train lengths to six cars and to maximize passenger capacity per car.  Five-abreast seating reduces the crew cost (and other operating costs) per available seat.
   
• Future-proof HSR compatibility.  Because the CHSRA has already settled on a single-level train architecture for its high-speed trains, it is likely that similar capacity limitations will drive the future California trains to be extra-wide, like the Japanese Shinkansen or the Russian Velaro.  Converting Caltrain to a wider standard helps achieve future platform interface compatibility with HSR, which is not just a matter of height but also of width.
   
• Easier conversion to high platforms.  Wider trains can be fitted with both high and low doors to accommodate a platform transition period, without cutting as badly into the seat count as for a normal size train.  (The Russian example is built exclusively for high platforms, but more doors could be added on the lower level.)  What's more, with high platforms built further away from the tracks, those annoying freight trains get a little bit more clearance.
    
• Easier vehicle packaging.  From an engineering standpoint, modern EMUs are like a jigsaw puzzle where every vehicle component must find its place under multiple constraints.  More width gives vehicle designers more flexibility to make everything fit, making trains more comfortable and maintainable.

There is very little downside to going wide.  Caltrain's EMUs would be a captive fleet on the peninsula rail corridor, such that expanding a few inches outside the AAR Plate F loading gauge would require only minimal infrastructure modification and would not impede interoperability.  Stadler has once again demonstrated that the car body shells of a modular vehicle can be tailored to any desired size, using different extruded aluminum shapes.

Caltrain should make full use of the generous clearances available on the peninsula corridor.  In a blended future where HSR limits the number of peak-hour commuter trains, extra-wide EMUs with five-abreast seating are an attractive solution for giving Caltrain more rush-hour capacity.

[Update 08/2014: this Swedish academic paper analyzes the numerous advantages of extra-wide trains in far more detail, going into cost elasticities etc.]