Capacity of Transit Vehicles

Often times, one of the main things that gets thrown around in bus vs rail debates is that rail has higher capacity. Is this inherently true? What does this actually look like? This is a blog post to illustrate that.

This is a general guideline for vehicles that are likely to be used in rich Western countries. Excluded from this list are things like 100% high-floor street vehicles, which are popular in South American BRTs but have generally been avoided in the developed world because level boarding then requires you to build lots of high-platform infrastructure. This is also not an exhaustive list, because I have no patience to list every possible transit vehicle that has ever existed.

Capacity in this list measures both seated people and standees. First, let’s cover vehicles intended to be used on city streets.

Buses

A standard city bus in North America is 40 feet, and a common 40 foot bus is the XD40. This bus has a capacity of ~80 people.

An articulated city bus in North America is 60 feet, and a common 60 foot bus is the XD40’s sibling, the XD60. This bus has a capacity of ~120 people.

Bi-articulated buses are common to South American BRTs, and are used in Europe, but the only current North American implementation is a future one in Quebec City. Wikipedia says a bi-articulated bus from Van Hool is 82 feet long and holds ~180 people.

Streetcars

The Inekon Trio-12 is a 66 foot long streetcar used in Seattle, that has a capacity of ~140 people.

The Bombardier Flexity that is used by Toronto is advertised by Bombardier as having a maximum capacity of 251 people at a length of 100 feet.

Limits that govern street-vehicle capacity

Buses generally have to be shorter than streetcars because they are not tied to rails, which makes steering each additional back section progressively harder. Buses also maintain the ability to swerve in and out of traffic, so bus drivers more so than streetcar drivers need to be paying attention to vehicles around and behind them, something that gets harder as a vehicle gets longer.

Streetcars can be very long, but both streetcars and buses are limited to the shortest distance between two intersections that can’t both be blocked at the same time; blocking two major intersections at a time with one vehicle would cause traffic jams.

Why do streetcars have higher capacity than buses?

1. Less seats = more room to stand.

Here is a comparison of the ~60 foot vehicles used in Seattle, which operates both streetcars and buses.

The interior of a King County Metro bus.
The interior of a Seattle streetcar.

You’ll notice that the streetcar has a lot less seating. Generally speaking, more people squeeze together standing up than sitting down. Also notice that the streetcar has a lot more for standees to hold onto.

Depending on what the goal of your transit vehicle is (are you serving mostly commuters who take long trips to downtown? Have you run out of vehicles and still need to squeeze more bodies on?) the seating vs. standing debate should be resolved for each application.

2. Door placement

In Seattle, the streetcar and some bus lines use proof-of-payment (POP) where you pay before you get on. However, the streetcar is optimized for this operation with large doors at the center of the vehicle, while buses still rely on narrower doors with awkward placements shifted for the front; this is because traditionally, buses required paying on board within sight of the driver.

For high-capacity applications, doors should be

  • wide, so that multiple people can get on and off at the same time
  • towards the center of the vehicle and equally spaced out, so that you minimize the walking distance to doors

This minimizes the amount of time that you have to spend at the stops, increasing throughput, which we will talk about in a later section.

Many operators in the US now use POP for some bus lines but the vehicles are not reconfigured to reflect this fact.

Subway-like “trains”; high-thoroughput and shorter trips

I use the words “trains” in quotes because at the end of the day, a train is basically just a bunch of individual cars coupled together that can be run without needing a driver on every single individual car.

Generally speaking, the limit of a train’s capacity is the platform length; because this is an NYC related blog, train capacity will thus show their normal length, the NYC subway length of 600 ft (and half-length of 300 ft), and the LIRR 12-car length of 1020 feet.

The AirTrain JFK is a medium capacity metro that uses ART Mark II rolling stock. At ~113 feet in length in a 2-car configuration, it has a capacity of 264 people. Extrapolated to 300 feet, 600 feet, and 1020 feet, this is a total capacity of 700, 1400, and 2383 people respectively.

Seattle Link Light Rail is purchasing S70 streetcar vehicles coupled together into 2, 3, and eventually 4 car sets. At 95 feet they carry 243 passengers each; extrapolated to 300, 600, and 1020 feet, these would carry 767, 1534, and 2609 people respectively.

The R160A is a standard trainset used in New York City’s B Division subway. A 5-car, 300 foot train carries 1281 people, and extrapolated to 600 and 1020 feet that is 2562 and 4355 people respectively.

Commuter/regional trains; longer trips that need more seating

These types of trains generally run on the “mainline” national rail network, which generally gets built with larger dimensions than standard subway trains.

The LIRR’s M7 runs in married pairs (2-car sets) 170 feet long with 211 seated passengers. Standing capacity is not available for these cars, but the 3×2 seating layout leaves almost no standing room anyways. Extrapolated to 300, 600, and 1020 feet that is 372, 745, and 1266 people respectively.

Thameslink in London runs a long regional rail network that feeds into a central tunnel in London, with some routes over 100 miles in length. The Class 700 they use has plenty of seating with a 2×2 configuration, but has room around the doors to stand, poles for standees to grab onto, and open gangways. An 8 car train exists at 531 feet with capacity for 1246; extrapolated to 1020 feet, that is a capacity of 2393 people. Keep in mind that there is also a separate first class car on these trains that generally has no standees and much larger seats; a fully standard class train would have more capacity.

London Overground is a short-distance regional rail network serving orbital routes that don’t pass through Central London. It uses all “bench” seating Class 710s, which carry 882 people on a 337 foot long train. Extrapolated to 600 and 1020 feet, that is 1570 and 2669 people respectively.

Why is the capacity of a single vehicle more important? Can’t you just throw more vehicles at the problem?

Not really. For a Western transit agency, labor is probably the most expensive part of running a transit trip. The larger vehicles are inherently more labor-efficient, up to a point; a train with two employees onboard is less ideal than one, but is still far more labor efficient than an equivalent amount of buses. (This is less true if you have a handful of collectors onboard each train just for punching tickets, like the LIRR, but that’s another article for another time.)

Where I now live, in Seattle, we have probably run into the upper limit of “how many buses can you throw at the problem”; we can no longer hire enough bus drivers to actually run the scheduled services, let alone the additional services that voters approved tax increases for, and the buses are getting caught in bus congestion despite having a four-lane street mostly to themselves. Now we are frantically building rail to try and replace buses with more labor-efficient vehicles.

Individual vehicle capacity is not the only metric, though; a line’s throughput of people per hour is also important, but that’s for another article.

And to end this, since I basically just spewed out a bunch of numbers and pictures, here’s a handy little infographic showing vehicle capacity relative to a 120-seat articulated bus.

Posted in 2020

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