SP-4: Investigate and Compare Methods Testing the Crashworthiness of Wheelchair Seating Systems and Peripheral Devices

Importance of the problem

Description of the need and target population

In 1990 the US Congress enacted the Americans with Disabilities Act (ADA) prohibiting discrimination against people with disabilities in employment practices, public accommodations and telecommunication services (ATBCB,1991). Transportation services by legislative definition fall within the public accommodation category. Therefore, public and private transportation service providers must accommodate persons seated in their wheelchairs who wish to travel. More recently the 2001 New Freedom Initiative has cited integration of persons with disabilities in the workforce and the community as a priority, specifically noting ‘transportation’ as a critical factor in meeting this priority (Whitehouse.gov, 2001). In support of the Initiative, the Director of Project Action reinforced this need indicating that one third of the 25 million transit-dependent people with disabilities report inadequate transportation as a significant barrier to integration. Such governmental priorities will continue to escalate the numbers of wheelchair users seeking transportation.

Wheelchair users who are unable to transfer to a motor vehicle seat during transport must rely upon their wheelchair to function as a vehicle seat. Unfortunately, design characteristics that make a wheelchair suitable for mobility often are in direct conflict with characteristics that define an acceptable motor vehicle seat. Typically, wheelchairs are intended to serve as a "mobility aid", while motor vehicle seats are designed to secure their restrained passenger or driver to the motor vehicle, which in turn provides mobility. Motor vehicle seats also incorporate numerous design features that protect an occupant in a crash and, accordingly, extensive research has been dedicated to the design and development of vehicle seats (Warner, 1991; Viano, 1992; Strother, 1987; Saczalski, 1993; NHTSA, 1997; Blaisdell, 1993; Adomeit, 1979; Aibe, 1982). Motor vehicle seats must also meet stringent government Federal Motor Vehicle Safety Standards (DOT, 1993). Unfortunately, only limited effort has been devoted to-date to the research, development and design of wheelchairs and their seating systems intended to serve as vehicle seats. In some cases, improper restraint has been shown to induce injury and even fatality in vehicle accidents (Bunai, 2001).

The recently adopted ANSI/RESNA WC19, Wheelchairs Used as Seats in Motor Vehicles, standard evaluates the crashworthiness of wheelchairs used as seats in motor vehicles (ANSI/RESNA, 2000). Testing required by this standard subjects a wheelchair-seated, 50th percentile male, Hybrid III test dummy to a 20g/48kph (20g/30mph) frontal-impact sled test. WC19 test criteria assess wheelchair integrity, as well as occupant and wheelchair crash kinematics. Despite an effort by ANSI/RESNA WC19 to evaluate complete wheelchair crashworthiness, seating systems are often added as after-market products. Wheelchairs utilizing after-market seating systems may, therefore, not be sled tested to evaluate their ability to withstand crash level forces. Additionally, replacement seating systems provided in the field that differ from those provided with a WC19 tested wheelchair will invalidate WC19 certification and will not have been tested. Therefore, test methods to evaluate wheelchair seating system crashworthiness, independent of the numerous wheelchair frames that it may be coupled with in the field, would promote increased safety and availability of transport seating systems.

Beneficial impact on target population, including service providers

Wheelchair users who cannot transfer to vehicle seats must remain seated in their wheelchairs, using them as motor vehicle seats during transportation. However, in most cases, wheelchairs have not been designed to serve as motor vehicle seats and wheelchair components may not be able to withstand the loads associated with crashes. The level of protection that wheelchairs and their seating systems provide under impact is, in many cases, unknown (Leary, 2001).

Vehicle seats are key to protecting occupants in a crash and accordingly motor vehicle seats have been designed to maximize occupant protection (Warner, 1991; Viano, 1992; Strother, 1987; Saczalski, 1993; NHTSA, 1997; Blaisdell, 1993; Adomeit, 1979; Aibe, 1982). Motor vehicle seats must undergo extensive testing to assure that they meet crashworthiness and occupant protection regulations as described by the Federal Motor Vehicle Safety Standards (FMVSS) (DOT, 1993). Seats must be secured to the vehicle and maintain their integrity so as to not load the occupant during a crash. Vehicle seats and hardware must be designed and constructed to provide support and reduce injury to their occupant under impact loading and rebound. When functioning as a motor vehicle seat, wheelchair seating systems should provide a similar level of occupant protection. Testing of wheelchair seating systems and its components independent of a specific wheelchair will promote increased safety, as well as increased availability of transport-safe seating. Currently, service providers and consumers are limited in their selection of transport-safe seating since only those seats which have been sled impact tested with a WC19 approved wheelchair are designated as transport-safe by wheelchair manufacturers. In addition, little is known about the safety and little guidance exists for use of various postural support devices on wheelchairs used as motor vehicle seats.

Responsiveness to priority

Tasks SP-4a and SP-4b respond to the priority to “investigate and compare methods, including low-cost methods, for testing, both static and dynamic, the crashworthiness of after-market and customized wheelchair seating systems and peripheral devices and, if found to be viable, develop strategies for integrating these into existing voluntary wheelchair performance standards,” as well as the priority “investigate the use of new or existing voluntary performance standards that would address problems associated with wheelchair-seated occupants……, and after-market and customized wheelchair seating systems and peripheral devices.”

Overall objectives

The objectives of the tasks addressing this priority are as follows:

1. Further development and refinement of dynamic test methods to evaluate seating systems.
2. Comparison of results generated using previously developed static test methods and newly developed dynamic test methods evaluating seating systems and components.
3. Identify key questions/concern regarding the use of secondary postural support devices (PSDs) during vehicle transportation.
4. Characterize injury risk or benefit associated with the use of PSDs.
5. Develop guidelines, and design and performance criteria for PSDs used in transport.
6. Transfer recommendations and findings to standards development efforts.

Last updated: March 17, 2002