There is a widespread assumption that urban transit should develop incrementally, progressing from bus to light rail to heavy rail, with the success of each mode justifying the viability of the next.

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This model of development is ahistorical, if not revisionist. We know that historically profitable rail transit thrived long before buses arrived on the scene. Moreover, there are essentially zero documented cases of high ridership bus routes evolving* into rail lines; as Eva Wood et al write, “no known conversions from BRT to LRT have occurred” (2006).

– We know that rail-first development can result in a sustainable urban fabric that supports high transit ridership (e.g Tama Garden City ). – Urban fabric resulting from bus-first development has a mixed record ( Curitiba may be the only success story?) – The smart thing would be to leave it there; the systems involved are so complex that self-deceptive rationalization is far more likely than true understanding. Wiser to accept that “trains first” is the historically proven model than to talk ourselves in circles with theories. – That said, here is some theory: – The key difference between trains and buses occurs at the stations; rail stations improve walkability , while bus stops generally do not. – Within one block of a rail station is a high value “direct access” (直接) zone with high foot traffic; within one block of a bus stop is a high noise, high pollution “diesel” zone with comparatively low foot traffic. – The natural result is that the articulation/clustering of walkable density around train stations is much higher than around bus stops. – Rail stations provide sufficiently concentrated foot traffic to support pedestrian oriented commercial life, thereby creating a convenient environment for car-free living, with broad appeal. This is the virtuous circle by which rail transit generates its own ridership. – The high capital costs of rail greatly increase the likelihood of joint transit+property development. The high cost of grade separated stations promotes greater stations spacing, vastly increasing their chances of achieving a critical mass of foot traffic at any one station. Moreover, the cost and quality of rail justify smaller lot sizes (i.e. fine-grained development), another key ingredient for walkability. –

The greatest weakness of bus routes might be their relatively low cost; it is too easy to trade frequent service for wide coverage, and it is too easy to add stops; spreading out boardings reduces the ability of any one stop to support pedestrian oriented commerce. The result is that bus systems usually do not promote articulation/concentration of commerce and the built environment.

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*In fact, there are several BRT systems for which conversion to rail is actively being planned (e.g. Bogota ). However, the rapidity with which these lines achieved high ridership indicates that they may as well have started out as rail; the conditions justifying rail development evidently existed before the implementation of BRT, not primarily as a result of BRT+Property joint development. Curitiba may be the lone exception.

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Curitiba’s implementation of BRT has been extremely successful, and holds many (mostly unheeded) land-use and zoning lessons for North American transit planning. It is the absolute poster-child for BRT. However, it is not an example of bus to rail evolution; despite carrying over a million passengers as early as 1990, the long awaited dream of rail conversion has yet to materialize.

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The Ottawa BRT is relatively successful within the North American context, but its success is largely dependent on an urban fabric originally built on rail transit; “ in 1929, the Ottawa Electric Railway carried more than 30 million riders on 90.5 kilometres of track.

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Related Reading

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