Once more into the bus/rail breech, my friends.
In various comments and articles, I’ve enumerated various advantages that bus rapid transit has over equivalent-service rail in some circumstances; this post is simply a collection of these. It doesn’t constitute an endorsement of bus over rail for any specific project or system, hence the word “may” in the title–that analysis needs to be done on a case-by-case basis. And this is a one-sided post; the corresponding advantages that rail has over bus are not listed. Not because they don’t exist or are not important, but simply because I wanted to collect many of the good technical pro-bus arguments in one place. (I’m limiting myself to technical arguments for the most part; sociological or political arguments such as “trains cause gentrification” or “rail is just pork for developers” are not included).
A bit of terminology: This article refers to “Class A”, “Class B”, and “Class C” transitways, which refer to the isolation of the transitway from other traffic. Very roughly:
- Class A is a grade-separated transitway (or one with absolute crossing priority), such as the various freeway-adjacent sections of MAX, and much of the Blue Line between Beaverton and Hillsboro. There are no examples of class A bus in the Pacific Northwest; North American examples can be found in Ottawa and Pittsburgh.
- Class B is surface operation in an exclusive right of way where the transit vehicle may need to stop at crossings, such as MAX through downtown, along Interstate and Burnside, and in downtown Hillsboro. Much of the EmX line in Eugene is an example of Class B BRT.
- Class C is ordinary mixed traffic operation–such as the bulk of TriMet’s bus operations as well as the Portland Streetcar. Generally, plain class C bus is not considered BRT, but a type of bus service that is is commonly referred to as class C+ bus (or by other names such as “rapid bus”)–this refers to mixed traffic bus that enjoys enough enhancements (off-board fare collection, all-door boarding, signal priority, limited stop spacing, prominent stops) that it is a materially better product than local bus. Mixed-traffic streetcar systems can also have signal priority (and be class C+); the Portland Streetcar does not do this however.
A claim was made in a thread at Human Transit that for class A and B operation, rail is almost always preferable; this is a partial rebuttal to that, but the content is important enough to emphasize that it deserves a post of its own.
After the jump…
BRT enjoys these advantages over rail:
- Topology advantages. One thing that BRT does easily but rail cannot do is operate in an “open” configuration–meaning vehicles travel in a transitway for part of their journey, and then filter out into the existing street network without need for any special off-transitway infrastructure. Trains can only run where there are tracks and switches, but busses can mix between a busway and local operation. Open BRT isn’t useful for every situation–it works best in cities with the main transit nodes concentrated in one place and transit demand dispersing outward from there–but many cities do have that transit topology.
Related to the open busway issue is the capability to handle large number of discrete vehicles. I’ll ignore some of the more extravagant claims concerning high-traffic freeway bus lanes like the Lincoln Tunnel XBL (Exclusive Bus Lane) between Manhattan and New Jersey; the XBL is a special case (there are no stops in the tunnel, after all). But here in Portland, the transit mall is able to handle–easily–180 busses per hour and 10 trains per hour, in each direction. Even if both 5th and 6th streets were dual tracked, and MAX trains limited to a single car-length, I can assure you that the Mall could not handle 180 trains per hour. For a long corridor–say Gateway to downtown–you wouldn’t want to run 180 busses per hour; if you had that much demand over such a distance that’s an obvious candidate for rail. But for highly branching topologies, the high vehicle throughput is a major consideration.
- Partial operation: The ability of busses to run on ordinary streets has a second set of advantages. It permits easier phasing–agencies building a busway or bus lane can open half of it when it’s done, and have busses run in the completed sections of the busway and on local streets the rest of the way, and then shift additional sections of the route into the busway when it completes. BRT also lets you get around hard parts with mixed traffic operation. Obviously, mixing in a mixed-traffic (class C) section adversely impacts the overall reliability of a route, but it’s a way to utilize existing (expensive) infrastructure such as bridges or tunnels. Rail, OTOH, can only go where there are tracks, and mixed-traffic operations compromises rail far more than it does bus.
- Costs. For Class C/C+ operation; bus is way cheaper to install–it’s just ordinarily local bus service, possibly with changes to traffic signals and nicer stations. The equivalent rail technology is mixed-traffic streetcar. Streetcar may be better suited to placemaking and land-use transformations, but the performance characteristics of mixed-traffic streetcar are generally the same as ordinary bus service; but streetcar requires installation of tracks. BRT also lets you do class B cheaply–if planners are willing to taking a traffic lane. Class A infrastructure will require major capital construction regardless of mode; a good argument can be made that rail is more suitable for class A operation for this reason (though that isn’t an open-and-shut case; Class A open BRTs like Melbourne are highly effective). But if political will exists, class B bus can be installed as cheaply as class C+. And even if a transit agency does decide to pour concrete–replacing asphalt with a road surface more able to withstand the axle loads of bus–you don’t have to relocate the utilities under the pavement or rebuild the roadbed. Which brings us to…
- Less prone to catastrophic failure. BRT doesn’t break down as easily or as spectacularly when the line gets blocked or closed. This benefit is most often discussed in the context of streetcars vs local bus (where obstacles along the route are plenty), but even class A and B transit lines are impacted by events such as accidents, breakdowns, power or control failures, and maintenance of the right of way. With a BRT, vehicles can simply navigate around, leaving the transitway if necessary. Rail often requires “bus bridges” to be set up when a line is taken out of commission. Generally, many sections of track–up to the next switch on either side of the incident–will need to be bridged. This happens all the time in Portland–and frequently results in bus runs being cancelled so a bus bridge can be assembled, angering just about everybody, both bus and train riders alike.
- The ability to pass. BRT makes it far easier to mix express and local services and provide skip-stop service. Busses can simply pull out of the busway for stops; only a little more pavement and real estate is needed to enable passing. The transit mall is a fine example of this capability, using skip-stop operation to achieve a high vehicle throughput.. Adding express tracks or passing sidings greatly complicates the design of a rail line, as switches need to be installed and signals changed for any change in track topology.