Almost all transit built
in the United States since 1980 has been ‘light rail transit’ (LRT)--but ‘light
rail’ is a regulatory classification for a vehicle, not a type of transit. The
term ‘light rail transit’ covers a wide range of types of propulsion, guideway,
and operating characteristics. A clearer articulation of the characteristics of
different light rail systems would help to better determine the relationship
between transit investment and associated outcomes.
The US is slowly
emerging from a transit Dark Age. The combination of subsidized competition and
public dis-investment effectively expurgated most urban passenger rail systems
from existence. It is necessary to re-invent, or rediscover, the constitutive
elements of effect transit systems. Historically, there have been many
different types of rail transit systems, but they fall into a small number of
distinct types, which might be called suburban railways, street railways, rapid
transit systems, and tram-trains.
Suburban railways link
major cities to suburban locations distant from the central city. They linked
independent towns to a nearby major city. Suburban railways are characterized
by high speeds and a very limited number of stops, and characteristically
bypassed the outer edges of an urbanized area to reach a central location. The
require exclusive guide-way, but their relatively infrequent operation (hourly)
means that this requirement can be met through temporary physical separation
(crossing gates) rather than the full cost of grade separation.
Street railways develop
from the horse-cart service. Initially steam powered, the nuisance presented by
the smoke and cinders meant that almost all systems were eventually
electrified. Acting more as labor-saving devices, they acted as a ‘pedestrian
extender’, rarely traveling much faster than a running man, and stopping
frequently. In Europe, the modern implementation is known as a ‘Tram’; in
America, as a ‘Streetcar’.
Rapid Transit systems
represent yielding to necessity. In locations where cost or difficulty of
obtaining sufficient surface right of way (viz: London, NYC, Chicago)
underground or elevated construction was necessary. Full grade eliminates the
need for sudden stops, making much higher speeds possible. The lack of cross-traffic
also makes much higher headways possible, so that it is possible to run a very
large number of trains on the same section of track. A bare handful of
metropolitan areas have been able to fund the construction of new rapid transit
corridors.
Tram-trains operate as
railways outside of cities, but as street railways within them. Adapted from
the ‘City-Rail’ system in Karlsruhe, Germany, it represents the revival of a
historical form of American transit, the ‘Inter-urban’. Inter-urban’s were passenger
rail lines running along freight railway right of way between cities, but on
city streets within the city. They represent an effort to reduce the friction
of transportation, by obviating the need for a mode-switch from train to tram
at the edge of the dense, pedestrian oriented central core.
Every implementation of
mass transit system represents a trade-off between cost, speed, and access.
Evidence suggests that the trade-offs are not entirely granular, but rather
represent a series of ‘market niches’ or functional classes of transit. The
same classes of transit emerge independently, repeatedly, in different
locations, at different times. Analyzing the characteristics of light rail
determines that there are ‘functional classes’ of LRT, with different service
characteristics, which resemble the service characteristics of historic transit
modes.