page_title: US Standard Light Rail Vehicle
section_title: Design
hierarchical_section_title: US Standard Light Rail Vehicle / Design
caption_attribution_description: English: Buffalo Metro Rail train at Erie Harbor Canal station in August 1988
context_page_description: The US Standard Light Rail Vehicle was a light rail vehicle built by Boeing Vertol in the 1970s. The Urban Mass Transportation Administration of the U.S. Department of Transportation promoted it as a standardized vehicle for U.S. cities. Part of a series of defense conversion projects in the waning days of the Vietnam War, the SLRV was seen as both a replacement for older PCC streetcars in many cities and as a catalyst for cities to construct new light rail systems. The US SLRV was marketed as and is popularly known as the Boeing LRV or SLRV, and should not be confused with their prior lunar roving vehicles for NASA.
  The US SLRV was purchased by the public transportation operators of Boston and San Francisco; in service by 1976, the US SLRV proved to be unreliable and scrapping started as early as 1987, but the US SLRV were not completely replaced in both systems until 2007. Although the SLRV itself was not successful due to poor reliability, it did set the general size and configuration for succeeding LRVs in the United States.
context_section_description: The SLRV is a double-ended articulated light rail vehicle 71 ft (22 m) long overall (over the anticlimbers) which rides on three two-axle trucks (six axles in total). The two end trucks are spaced 13 ft 6 in (4.11 m) from each end, and the center truck is under the articulated section, allowing a minimum track radius of 32 ft (9.8 m). The dimensions of the SLRV were determined by the existing track constraints of three proposed operators: MBTA (Boston), Muni (San Francisco), and SEPTA (Philadelphia). Each car has an "A" and "B" end separated by a central articulated section. Each side has three passenger doors 53 in (1,300 mm) wide: one near the operator's cab, and two straddling the articulated section; there is no door at the rear (trailing) cab (in the direction of travel). The tested empty weight of the vehicle (including 1,770 lb (800 kg) of instrumentation) was 69,130 lb (31,360 kg); for a normal load of 100 passengers, the vehicle was 82,500 lb (37,400 kg) and for the crush load of 219 passengers, the vehicle was 104,495 lb (47,398 kg).
  Each end truck carries a single DC motor which powers both axles and has a rated output of 210 hp (160 kW) at 1135 RPM, operating on 285 VDC; the traction motor drives the wheels through a reduction gear set of 5.571:1. In the original 1971 LTK design for Muni, the center truck was also powered, giving a top speed of 65 mph (105 km/h); in the final SLRV specification, the center truck was not powered and the top speed was reduced to 50 mph (80 km/h). Power to the traction motors is controlled through a solid state "chopper" circuit operating at a frequency ranging between 0 to 400 Hz for vehicle speeds up to 17 mph (27 km/h), allowing a continuously variable control of power from the 600 V overhead lines rather than the traditional trolley control at the time, which used a varied number of discrete resistances to control motor current. Above 17 mph (27 km/h), the power is not "chopped" and is instead applied directly to the traction motors.
  Primary dynamic braking is accomplished by running the traction motors as generators and dissipating the electricity generated through two brake resistor grids; a friction brake consisting of a single inboard disc brake per axle is blended with the dynamic braking as needed. The friction brake alone is sufficient to hold a fully loaded SLRV (with 219 passengers) on a 9° slope. In addition, six electromagnetic track brakes are provided; on the Muni cars, the track brakes are controlled independently to hold the car in place when starting on a slope, and on the MBTA cars, the track brakes are blended into the main brakes. Dynamic braking was enabled by using a separate power source to energize the field coils on the traction motors; Boeing stated that regenerative braking was possible. Although regenerative braking was not implemented on the SLRV, it was enabled on the similar CLRV.
  The articulated section allows up to 16° of rotation in the horizontal plane, 3° of vertical sag (center section lower than ends), and 4.3° of vertical crest (center section higher than ends), which permits the SLRV to traverse curves as sharp as 42 ft (13 m) inside radius, travel through valleys with a vertical curvature of 460 ft (140 m), and crest hills with a vertical curvature of 310 ft (94 m).
  The SLRV rolls on lightweight Acousta Flex composite resilient wheels 26 in (660 mm) in diameter; these wheels use aluminum hubs separated from the steel rims/tires by a silicone rubber cushion. The cushion is ³⁄₁₆ in (4.8 mm) thick and is injected in the threaded space between the rim and hub; the design was developed by Standard Steel and BART in the 1960s. The resilient wheels reduce squeal when negotiating tight curves. Interior noise was claimed to be 65 dB. The design of the trucks is adapted from the Japanese Shinkansen trains. The trucks are equipped with rubber chevron springs and pneumatic suspension, which automatically adjusts to maintain floor height with varying loads. Damping is accomplished by both hydraulic (lateral) and pneumatic (vertical) means.
  The car 
caption: Buffalo Metro Rail LRV by Tokyu (1988)
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