Memorandum - NHTSA

IV- 1 9
than 3 inches off the ground. The outer barrier is the only safety device which can prevent a
wheelchair occupant from accidentally falling from a raised platform and research has shown
electric wheelchairs are capable of climbing over some barriers which are in use today. Lifts ( an
achieve a height of 40-50 inches off the ground, depending on the bus‘s floor height with the
result that the top of the head of the wheelchair occupant could be a total of 90-100 inches off the
ground. A fall could cause serious injury. All lifts are designed with a wheelchair retention
device regardless of intended vehicle GVWR. The Final Rule requires a dynamic test,
employing a WC test device, to prevent the WC from climbing over the outer barrier, and an
overload strength test to prevent the WC crushing, bending or plowing-through for the
wheelchair retention device.
In their final guidelines issued September 6, 1991,the Access Board did not specify a safety twt
for the outer barrier or WC retention device, but deferred to NHTSA’s expertise, as the agent!:
was planning to issue proposed safety standards for lifts. In the Access Board’s final rule it is
stated (pg. 45535), “...the Board feels that NHTSA is the appropriate agency to define safety
tests .’,
New WC Retention Test Method
The WC Retention Device or outer barrier can be defeated by (a) WC climbing, (b) loss of
strength and rigidity or (c) WC tipping. The WC retention device test is designed to address t le
first two failure modes: (a) if traveling too fast, in the rearward direction, the large wheels of tine
wheelchair can climb-up and over the outer barrier resulting in occupant injury and (b) if