Bus capacity : some remarks

November 9, 2012

Pretty often, you can see in the news that double articulated bus have extraordinary carrying capacity, e.g. 300 passengers [1], news somewhat used by advocacy groups or lobbyists to promote their idea. The point is that the capacity number refers to a context, be South America or China, where bus occupancy standard could not be at par with the ones seen in North America [6]. This need to be placed into a proper context:

The “Normalized” bus capacity curve

The curve below uses a capacity index normalized at 1 for the staple 40 foot bus, rather than an absolute pax capacity. This curve has been essentially drawn from number collected from the LACMTA which has a fleet including 40″, 45″, 60″ and 65 foot buses, and other correlations to deduce that the bus capacity as function of its length is looking like it:

Capacity of a bus as a function of length

The curve begs explanation:

There is lot of “dead” space in a bus, bus driver space, wheel’s room…which will impair its capacity. As well the interior configuration and doors can affect the circulation inside the bus (usually a bus carries less pax per sq meter rear of its back door). The bus articulation area is a kind of a dead space of its own too, and it is usually 5 feet long…The scheme below illustrates the issue:

Different common bus length, top bus is a NewFlyer D40LF for reference, bottom is a Van Hool AGG300 in a custom design (mettis) for Metz, all others are Mercedes Citaro buses in different lengths

The bus articulation joint leading to an sub-optimal use of space is also

  • an additional source of maintenance.
  • and additional constraint on door location (leading to additional dwelling inefficiency)

Due to the above, transit agencies could look at buses with extended body rather than more articulations. The bus maneuverability is usually maintained by rear wheels steering [2], a relatively common occurrence on European bus 45ft or longer.

The doors configuration

Step free bus interior with door behind the rear axles is a relatively common occurrence seen in Europe: The reason is to encourage people to occupy the rear of the bus, and offer a better load partition along the whole bus length. That leads often to 3 door 40ft+ bus and 4 door 60ft+ bus, which have the other advantage to improve the dwelling time:

A 3 doors, step free floor (Lyon ETB12 on left), removes circulation barriers and allows a better load partitioning of the bus than a more traditional setting (New Flyer D60LFR Translink) - credit photo (5)

But there is more to doors: outside opening doors could be preferred to the ones consuming precious interior space [3]:

An iris-bus with outside sliding door

Additionally, they don’t interfere with passengers in overloaded bus, allowing faster opening/closing operation. The freed space can allow more optimal organization of the interior space:

Inside of an Irisbus Crealis (OEM model): door opening on the outside open space in the inside.

Notice that the UK agencies, like the Hong-Kong companies, in general adopt a different policy than the continental Europe ones in regard of bus doors. Pretty often bus come with a single large door, which has the advantage of discouraging fare dodger, allows more seating spaces, and less strain on the bus HVAC system. Paris’ RATP used to have 3 door 40ft and 4 doors 60ft, but eventually reverted to 2 door 40ft and 3 door 60ft in an attempt to discourage fare dodger

The double decker bus

In theory, it offers a tremendous capacity. But, beside the room taken by the stairwell, the separation of space on two levels prevents an optimal partitioning of the load. However, one of the main drawback of the double decker is considered its longer dwelling time making it a solution less interesting than articulated bus in normal urban condition[4].
That said, most recent double deckers, as the one illustrated here, the new London bus, NB4L (37 feet) or the Man Lion’s city DD (45 feet) and improved the dwelling time, by having to stair well (providing a good circulation on the upper deck) and 3 doors

In despite of pure geometric drawback as noticed above, The question of the relevance of the double decker bus need to be kept open, since people tend to like it, and there is at least 2 reasons for that:

  • It offers 2 different spaces, usually a quieter one on the top deck, ideally suited for longer journey
  • It offers greater comfort than artics bus, especially rear of artics bus

Those reasons able to attract more customer, in addition of operating advantage (it make a better use of road/curb/yard space) can offset other drawbacks as noticed above.

An embryon of this post had been posted on SPP in 2010. It is written in the context of addressing the Vancouver Broadway capacity issue

[1] World’s Largest Bus: China’s 300 Passenger Youngman JNP6250G Set to Serve Beijing and Hangzhou, June 17, 2012

[2] this video illustrates it

[3] this video illustrates it

[4] That is at least the conclusion of the consumer group London travel watch as cited by wikipedia,

[5] Lyon’s ETB12: www.t-u-f.org, Translink NewFlyer D60LFR: translinkphotos.webs.com

[6]Lacmta estimates the capacity of its 65 footer at 100 pax. The constructor, Nabi, will come up with number at 71, while in Bratislava, a similar bus length will be considered able to carry 200 pax. Bi-articulated buses operate more often than not in area having generous standard for bus capacity closer to the Bratislava than the Los Angeles one.