There is debate about the relative merits of investing in rail or express bus modes to improve regional transit performance. The debate largely assumes that both modes serve a single function of providing higher speed service to the central business district (CBD) over relatively long travel distances. The debate generally overlooks other functions that might be served by express bus and rail transit modes and thus ignores that the two modes may perform differently depending on the service mission they are assigned. Performance of the two modes is examined in four metropolitan areas with different strategies for providing high-quality, regional transit service: a CBD-focused strategy, a hybrid strategy that serves the CBD and a few other destinations, and a multidestination strategy that serves a widely dispersed set of destinations. ... It was found that the combination of a rail transit backbone and a multidestination service strategy leads to better performance than any other marriage of mode and mission.
In other words, (a) rail and bus technologies are tools, and no tool is right for every job, and (b) multi-destinational networks based on connections are more productive than radial systems that narrowly focus on a single downtown. Regular readers of this blog will find these conclusions obvious, but it's interesting to see that this argument still needs to be made in the literature.
UPDATE: Let me tease this apart a little further. I don't mean to imply that the work is redundant, but it does apply to a narrow range of cases, and it conflates "multi-destinational" with "rail" a little more than I'm comfortable with.
The authors' focus is on four cities which they locate on a spectrum from "CBD-oriented" to "multi-destinational."
- Pittsburgh, which they identify as the most "CBD-oriented."
- Minneapolis, which they identify as transitional or hybrid.
- Atlanta and San Diego, which they identify as "multi-destinational."
These cities are all comparable in size, all have a mix of rail and bus, and all have some facilities for getting express buses out of traffic at least some of the time, ranging from the full busways of Pittsburgh to the freeway-shoulder operations of Minneapolis.
A CBD-oriented system (more commonly called a radial system) is one that views downtown as the sole destination of importance. In such a system, people who aren't going downtown usually have to go via downtown, whether or not this is on the way. A multi-destinational system is one that tries to serve trips to many destinations all over the city. If you live in Los Angeles or Manhattan or Paris or Berlin, this distinction will seem silly to you, because your city has been multi-destinational for decades if not centuries and your transit system adapted to that reality long ago. But most American (and Australasian) cities had a period, generally ending around 1945, when they had a single extremely concentrated downtown -- fueled, in many cases, by streetcar/tram networks that converged on it. And at one time, it made perfect sense that this downtown would be the sole focal point of the transit network.
Since 1945, most cities have been becoming more multi-destinational, with more important destinations (employment, retail, leisure, etc) scattered all over the city. Transit agencies were generally slow to adjust, especially since downtown tended to be where they were most appreciated and where the pre-car development pattern made it easy for pedestrians to get to them. But over time, it's been necessary to adjust to a multi-destinational pattern in order to remain relevant to the life of the city as it is now. The paper suggests that of the four cities studied, Atlanta and San Diego are relatively far along on that path, Pittsburgh least so. (This seems to match Alan Hoffman's observation (here, page 67) that despite the introduction of busways, the Pittsburgh network has changed relatively little for a long time.)
Note that the important distinction here is not that the network infrastructure is more or less CBD-oriented, but that the thinking of the transit agency is. All four of the cities studied have CBD-oriented transit infrastructure that suits their CBD-oriented history, but they have thought about their networks in different ways.
By comparing the experience of these four cities, the authors find that the most effective system is not the CBD-oriented but the multi-destinational. Needless to say, your mileage may vary; it depends on how CBD-oriented your city still is, but even a city as CBD-oriented as Portland had great success with a multi-destinational network. Most of the major network redesigns I've done have been about helping CBD-oriented systems still meet their CBD need while also being relevant to a wider range of destinations.
My only quibble is that multi-destinational systems don't have to mean "rail and bus working together" because you can do the same thing in smaller or pre-rail cities by designing an all-bus system to work just the way a good bus+rail system would work. I was the lead planner on a redesign for San Antonio around 2001-2, shortly after their voters had rejected light rail. We did what we could to create a connective frequent network given that they only had buses to work with. Following Portland's model, we did this with a mixture of high frequency grids in the denser inner city and trunk-and-feeder systems in the outer suburbs. As a side effect, that project helped to intensify and simplify services in a concentrated corridor (Fredericksburg Road) where they're now planning Bus Rapid Transit, and light rail is being talked about again.
Portland, too, did it with buses first. Their multi-destinational route network (including the frequent grid covering the inner city and the trunk-and feeder structures for major outer suburbs) all were put in place by 1982, four years before the first light rail line opened. Rail sometimes leads, but sometimes the result of good multi-destinational network planning, not its cause or starting point.