Light rail vehicles are built in a variety of designs and dimensions. In almost all cases, they are capable of being operated in coupled trains. Modern LRVs are generally much larger and heavier than their streetcar predecessors and can have axle loads just as large as, or even larger than, so-called "heavy rail" transit vehicles.
Light rail vehicles vary in the following design characteristics:
- Unidirectional versus bi-directional
- Non-articulated versus articulated and, for the latter, the location(s) and configuration of the articulation joints
- 100% high-floor versus partial low-floor (typically 70% or less) versus 100% low-floor
- Overall size (width, length, and height)
- Truck and axle positions
- Weight and weight distribution
- Suspension characteristics
- Performance (acceleration, speed, and braking)
- Wheel diameter and wheel contour
- Wheel gauge
These characteristics must be considered in the design of both the vehicle and the track structure.
2. Non-Articulated/Articulated
The earliest electric streetcars in the 1880s were four-wheeled single truck vehicles. Streetcar
ridership quickly outgrew the capacity limitations of such vehicles, and eight-wheeled double truck
streetcars were common by 1900. Often, these larger cars would pull a trailer car for even more
capacity. The first articulated streetcars appeared in the United States about the time of World
War I, often by splicing together two older single truck cars, and later as three-truck vehicles
functionally very similar to high-floor, articulated LRVs of today. The objective of this evolution in
vehicle design was to maximize not only passenger capacity but also the number of passengers
carried per operating employee since labor costs, then as now, were a high percentage of the
cost of transit operation.
That trend has continued up through the present with the result that multiple-section light rail vehicles have reached unprecedented lengths. Today, with the exception of legacy and heritage streetcar operations and three light rail systems that bought new rolling stock in the 1980s, all new and modernized North American light rail systems are using articulated cars with two, three, or more carbody sections. Two-section articulated LRVs, which were the most common design when the first edition of the Track Design Handbook for Light Rail Transit was published, are now being purchased only for those LRT lines that require a 100% high-floor car to match highplatform stations.
The development of LRVs with multiple-carbody sections (up to seven sections in the case of trams purchased in Budapest, Hungary, in 2007) was driven by the same issues as a century ago—carrying more passengers with fewer operating employees. Multiple-carbody vehicles also have fewer motorized trucks per passenger and thereby provide substantial energy savings. Several North American systems are following this trend. Toronto ordered new five-section streetcars in 2008. Dallas Area Rapid Transit, following a trend started in Europe, modified older two-section, high-floor light rail vehicles to add a low-floor center section. New Jersey Transit has investigated adding two additional sections to their current fleet of three-section, 70% low-floor cars.[4]
Where two body sections meet, a turntable and bellows arrangement connects the sections, allowing continuous through passage for passengers from one end of the car to the other. In the case of high-floor LRVs, a single such arrangement, centered over a truck of conventional design, is used to connect two carbody sections. Low-floor LRVs require two such articulations—one on each side of the center truck and center section of the carbody—since there is no room for the turntable above the special trucks required under low-floor cars. This usually results in a very short carbody section at each low-floor truck.
