LRT itself is a broad spectrum and ranges from single unit streetcars running in mixed traffic within city streets at speeds as slow
as 25 mph [40 km/h] and even lower up through multiple car trains running on a totally exclusive
guideway at speeds of 60 mph [100 km/h] or faster. The streetcar lines in New Orleans are
representative of the lower end of this spectrum while the Metrolink system in St. Louis is a good
example of the upper end. In much of Europe, these two extremes are often called “trams” and
“metros.” In Germany, the terms “strassenbahn” (“street railway”) and “stadtbahn” (“city railway”)
are commonly used.
It is important to note how, along any given light rail transit line, one might reasonably include
guideway and track elements that are very much like a strassenbahn while a short distance away
the route’s character might radically change into that of a stadtbahn. LRT is a continuum and,
within the framework of the operating requirements of a given project, the LRT track designer can
incorporate appropriate elements from each of the mode’s extreme characteristics plus just about
anything in between.
Light rail lines are fairly distinct from metro rail systems (often called “heavy rail”). The latter are
always entirely in exclusive rights-of-way, are usually designed to handle long trains of vehicles (6
to 10 cars per train is common) and have a relatively high absolute minimum operating speed
along the revenue route (usually 45 mph [72 km/h] or higher). By contrast, LRT trains can
operate in shared rights-of-way, very seldom exceed three cars per train, and speeds as low as
10 mph [16 km/h] are tolerated in revenue service track. These differences usually mean that
LRT can be constructed at far lower cost than metro rail transit, although the passenger
throughput capacity of the latter is also much higher.
If there is any one single characteristic that defines “light rail,” it is likely the ability of the vehicle to
operate in mixed traffic in the street when necessary. This draws a line between the St. Louis
example above and a light metro rail operation such as SEPTA’s Norristown high speed line. The
operational characteristics of each route are virtually the same, but only the St. Louis vehicle
could actually operate in the street if necessary. It is a very fine distinction, and, while purists
may quibble with some of the finer points of this definition.
Several rail transit projects have utilized diesel-powered light railcars (also known as “diesel
mechanical units” or “DMUs”), which do not meet FRA buff strength criteria. Except for the
propulsion system, many of these vehicles and the guideways they run upon closely resemble the
stadtbahn end of the LRT spectrum. The second edition of the Handbook will not attempt to
cover all of the nuances of the DMU mode.
Throughout this volume, the words “railroad” and “railway” will appear. By “railroad” it
mean standard gauge rail operations that are part of the general system of railroad transportation.
This includes freight railroads and passenger railroads (such as Amtrak and the commuter rail
operations in many cities). The word “railway,” on the other hand, is intended as a broader term
that includes all transportation operations that utilize a vehicle guidance system based on the use
of flanged steel wheels riding upon steel rails.
