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.
3. High-Floor/Low-Floor LRVs Getting passengers safely and expeditiously onto and off of light rail vehicles at stations has always been an issue. Time spent at stations—“dwell time”—can be a significant percentage of the overall running time from terminal to terminal. For a conventional “high-floor” light rail vehicle, with steps at the doors that are internal to the vehicle, the delays inherent in climbing up and down steps adds significantly to the dwell time. The various measures necessary to comply with the Americans with Disabilities Act Accessibility Guidelines (ADAAG) means even more delay before such LRVs can resume forward motion.
Level boarding from the platform to the vehicle is clearly the best way to accommodate the mobility-challenged transit rider. Level boarding also reduces station dwell times by making it easier and quicker for all riders, mobility-challenged or not, to board and alight from the LRV. Because of these advantages, heavy rail metro systems have always used level or near level boarding from high level platforms. Following that example, several light rail systems built during the 1980s, in both North America and Europe, incorporated level boarding from high level platforms, largely eliminating the need for steps.
The problem with high level platforms is that they usually can fit alongside of the tracks only if the light rail line is in an exclusive guideway such as a subway tunnel, an aerial structure, or a private right-of-way. High platforms that are the full length of the train (usually no less than 200 feet/60 meters for a two-car train) are generally impractical where the LRT guideway is in an urban street. Urban locations often also have insufficient space for vertical circulation elements to get passengers from street and sidewalk level up to a station platform that would usually be 3 feet [0.9 meter] higher. Moreover, a two- or three-car long high platform will often be very intrusive on the urban streetscape, as well as quite expensive.
Because of such issues, light rail systems that were constructed in the 1980s and early 1990s and included extensive operations in city streets typically used high-floor LRVs that were equipped with steps for patrons to board from sidewalk level. A variety of methods were used to get mobility-challenged persons on and off the vehicles, with mini-high platforms being the usual choice. However, these arrangements were generally less than fully satisfactory. Some means of providing level boarding for all riders without resorting to full-length high level platforms was desired.
