The following are some of the factors that should be considered when evaluating single-end versus double-end light rail vehicles:
Systems with stub-end terminals at either one or both ends of the line or at any intermediate turnback location will require bi-directional vehicles.
Bi-directional vehicles with two operating cabs and doors on both sides of the vehicle will cost more than a single-end LRV with only one cab and doors on only one side.
For slow speed movements in a yard or under an emergency situation, many single-end LRVs have a “back-up controller” in the rear of the car, often hidden behind a panel or under a seat.
Unless equipped with doors on both sides, single-end LRVs require that all station platforms be located on the same side of the tracks. Having doors on both sides of the vehicle provides the capability of having stations on either or both sides of the track, regardless of whether the vehicle has one operating cab or two.
Single-end vehicles that have doors on both sides can be coupled back-to-back resulting in a double-end train.
The choice of single-end versus double-end vehicles may have an impact on how yard and shop facilities are laid out. This in turn will affect the real estate requirements for that facility and hence its location. The yard location in turn may have a direct effect on the system operating plan.
Double-end vehicles typically have more uniform wear of the wheels since the leading axle on each truck changes at the stub-end terminals. Single-end vehicles often develop thin wheel flanges on the leading axle of each truck while the flanges on the trailing axles incur relatively little gauge face wear. This directly affects the frequency and cost of wheel truing and ultimately wheel replacement.
From a civil engineering perspective, stub-end terminals are less costly compared with the loops because, as noted above, of the land costs and other local space restrictions. Trackwork costs for a stub-end terminal versus a loop could be similar or greater depending on the configuration and amount of special trackwork associated with any terminal station, passing tracks, or storage tracks. Train control system costs are nearly certain to be greater for a stub-end terminal than for a loop terminal.
Stub-end terminals have construction and maintenance costs associated with special trackwork and train control systems that differ from those of loop tracks. The designer must evaluate options based on life cycle costs.
Dwell times for a loop terminal are appreciably less than those for a stub-end terminal, which can be advantageous at terminals with extremely close operating headways.
If double-end cars are selected, it is still possible to have loops at some terminals should local conditions make that choice advantageous.
Loop tracks are more likely to be sources of noise than stub-end terminals, possibly impacting both the wayside community and patrons alike. The crossover track movements associated with a stub-end terminal are more likely to be a source of groundborne vibration, particularly if a double or “scissors” crossover is used.
Loop tracks at an intermediate turnback point will require a crossing diamond, which is more likely to be a source of noise and vibration than the ordinary frogs in the crossover tracks associated with a center pocket track.
If there is a reasonable probability that a line might be extended beyond some initial terminal location, a stub-end track arrangement—and hence double-ended vehicles— would usually be the logical choice.
Stub-end tracks provide greater flexibility for vehicle storage during off-peak hours.
