GUEST EDITORIAL


Wheelchair transport safety--the evolving solutions

The Americans with Disabilities Act (ADA) and Individuals with Disabilities Education Act (IDEA), have provided, among many other things, more opportunities for all persons using wheelchairs to gain better access to public transportation. Advances in vehicle modifications and driving adaptions, specifically for vans, have increased the numbers of wheelchair users that utilize personal vehicles as either passengers or drivers. Because many people either elect to or must remain in their wheelchairs while riding in a vehicle, a number of issues related to the safety and security of the wheelchair-seated person are raised, especially in the event of a vehicle collision.

What Are the Issues?
Motor vehicle safety research has a long history involving governments and the motor vehicle industry throughout the western world. This research has clearly established a number of fundamental principles of vehicle occupant protection that, through implementation in vehicle design and industry testing standards, have drastically reduced the number of fatalities and injuries. In summary, these principles stipulate that occupant injury prevention must be considered as a system that includes the vehicle seat, the occupant restraints, and the interior of the vehicle. Since approximately 60 percent of vehicle collisions that lead to fatality or severe injury are frontal impacts, protection systems have been optimized to protect the occupant from injurious forces that can result from frontal impacts.

Dr. Hobson
Douglas A. Hobson, PhD,
Associate Professor
Department of Rehabilitation Science and Technology
School of Health and Rehabilitation Sciences
University of Pittsburgh
Pittsburgh, PA 15240

One critical design aspect of the occupant protection system is the relationship between the vehicle seat, the occupant, and the occupant restraint (lap belt, shoulder belt, and air bag). First, the seat is securely fastened to the vehicle and designed to hold the occupant in a limited range of body positions relative to the occupant restraint device(s). Second, this system is designed to limit and control the motion of the occupant relative to the interior of the vehicle during an impact event. When a person substitutes a wheelchair for a regular vehicle seat this protection system no longer functions as designed and the wheelchair occupant may be at significant increased risk of serious injury. In the case of a public transit vehicle, other passengers are also at increased risk if the wheelchair is not fastened securely to the vehicle, especially in the case of a heavy powered wheelchair.

Until most recently, wheelchairs have not been designed to also serve as occupant-protecting seats in a motor vehicle. For example, armrests and other frame structures often prevent the attainment of effective fit of the occupant restraint belts. In most cases the seat and wheel assemblies will not sustain the crash loads necessary to hold the person in the position necessary for effective occupant restraint. Accessories, such as seat inserts, positioning supports, and tray-mounted devices are often added to the wheelchair after they leave the manufacturer. These add-on accessories also are not designed with crash injury prevention as a goal. Many frame designs lack locations and the necessary strength for the attachment of the tiedown straps required to secure the wheelchair to the vehicle. And finally, until recently, there have been no industry standards to which the wheelchairs and their tiedown devices could be tested in order to ensure a level of injury prevention that approaches that achieved for persons using OEM vehicle seats and occupant restraints.

Prior to 1999, the wheelchair industry, largely for reasons of liability, elected to place stickers on their wheelchairs stating that their product should not be used as a seat in a motor vehicle. This placed many parents, school bus transporters, education systems, and transit authorities in a difficult legal position. For example, IDEA mandates that all children with disabilities must be transported to educational settings. The ADA mandates that all wheelchair users be given access to public transit. Insurance companies for transporters were increasing rates and denying coverage because of the increased liability they then faced. Parents were raising questions about the safety of their children on school buses.

The ADA stipulates that occupied wheelchairs on public transit vehicles must be secured to the vehicle in specified wheelchair stations and occupant restraints must be provided, but their use is optional. Given that the evolved industry standard for wheelchair securement is the four-point strap-type system, this now means that the vehicle operator must leave the operator station to secure and unsecure the wheelchair for each wheelchair rider. With no standard locations to attach the four straps to the wheelchair frame, securement is often inadequate and in some cases does not occur at all. Finally, operator unions are less than supportive of this additional role of the transit vehicle operator as mandated by the ADA.

Clearly, there was (and still is) a complex mix of issues that have been crying out for solutions for many years. Solutions are now evolving based on research and standards development that are involving a broad cross-section of people and organizations. One overarching concept has been that, to the extent possible, the solutions should be offered as safety options to wheelchairs users, since personal safety is most often an individual choice. And clearly, these evolving safety options must not be used as a means to limit access to transportation by transit authorities, but rather as a means to allow wheelchairs users, or their guardians, to increase their transport safety.

The Evolving Options
The Organizational Structure
In order to begin to address the diverse range of above issues and have the resulting outcomes implemented in a way that would make a lasting difference, a forum for discussion, consensus decision-making, and ideally worldwide implementation was necessary. The existing standards development activities within RESNA, the Society for Automotive Engineers (SAE) and the International Standards Organization (ISO) have proven to be an excellent forum in which to tackle these multiple issues. The standards development forum brings together the key people, such as researchers, the involved industry representatives, wheelchair users, and clinicians. The agreed-upon scope of the standard focuses the discussion. An imposed timetable stimulates closure on debate and the reaching of consensus. It can focus and facilitate collaboration of research efforts at both the national and international levels, as well as across the industries that market wheelchair products. In the case of transport safety, the common goal has been to develop industry-wide performance and testing standards that are based on the fundamental principles of vehicle safety research with emphasis focused on the safety needs of the wheelchair-seated rider.

The author was elected to lead the transport safety working groups within each of the three standards-setting organizations, which served to facilitate harmonization across the three working groups. In 1997, the SAE group completed the SAE Recommended Practice J2249, Wheelchair Tiedown and Occupant Restraint Systems (WTORS), which is now used by all major manufacturers producing four-point strap-type securement systems. The RESNA group completed the ANSI/RESNA WC-19 Wheelchairs for Use in Motor Vehicles in April 2000. The ISO-TC173/SC-1-WG-6 group has completed parallel standards for WTORS (ISO 10542, parts 1 and 2), and is in the final stages on ISO7176/19, Wheelchairs for Use in Motor Vehicles. Although there are some differences between the U.S. and ISO standards, harmonization has been achieved on the major requirements and performance tests. Wheelchair manufacturers have been actively testing their products to the WC-19 and 7176/19 standards and now have tested products available on the market. The "don't use on vehicles" stickers are no longer being placed on most wheelchairs.

The Early Research Efforts
To date, the research in support of the transport standards development has been a collaboration between research and test facilities in the United States, the Netherlands, Sweden, Australia, and England. In the United States this work has been pioneered by the University of Michigan Transportation Institute, directed by Larry Schneider, the RERC at the University of Pittsburgh, co-directed by Douglas Hobson and Gina Bertocci, and in the early stages, the University of Virginia, led by Greg Shaw. In the U.S., funding support has been obtained from multiple federal, foundation, and private sources. This collaborative effort has led to significant results to date. The background, current status, and work in progress are summarized below. Details of current research efforts are presented elsewhere in this issue.

A primary research focus has been to translate and verify the time-tested safety principles established by the motor vehicle industry to the situation of the wheelchair-seated vehicle occupant. The seminal test is the simulated crash test using an actual vehicle and instrumented test dummies (ATDs), which are subjected to a crash pulse of a predefined "g" and velocity change (delta V). The crash pulse used throughout the motor vehicle industry, and specified within the U.S. Federal Motor Vehicle Safety Standards (FMVSS), is 20 g, 30 mph (48 km/h) delta V. Measures of deceleration loads experienced by the ATD and displacement values are used to quantify the vehicle and occupant safety system performance.

For wheelchairs and their securement devices, a less expensive testing regime had to be developed and validated if it was to be acceptable as an industry performance standard. It was decided to use the same crash pulse (20 g, 30 mph) as the motor vehicle industry but generated by a dynamic impact sled, available at several collaborating laboratories. Displacement measures of a 50th-percentile male ATD and the occupied wheelchair during the simulated crash event, along with obvious structural failures, would be used to quantify the performance of both the tiedown and occupant restraint devices (WTORS), and the transport wheelchairs.

Because the WTORS industry is small, a method for crash testing WTORS had to be developed that did not require the destruction of a new wheelchair with each test. After considerable debate, agreement was reached on the design specifications for a surrogate wheelchair, that when occupied by the ATD and subjected to the standard crash pulse, would apply repeatable loads to WTORS devices being tested. Passing this performance test meant that the WTORS could be considered tested safe for use with any wheelchair up to a specified mass. After a two-year, multi-laboratory validation testing period this approach was accepted and is now the key test in both the SAE J2249-Recommended Practice and ISO 10542 standard.

Specifications for the Surrogate Wheelchair Used in the Dynamic Testing of Wheelchair Tiedown and Occupant Restraint Systems
Design requirements and performance testing of wheelchairs intended for use as seats in motor vehicles involves even more complex issues than the WTORS. In addition to the issues outlined in the introductory section, it is most desirable to have the wheelchair safely secured and the occupant appropriately restrained by any WTORS that conforms to the WTORS standards. One testing approach is to evaluate wheelchair performance using a surrogate WTORS that meets all SAE J2249 and ISO 10542 requirements. The alternative is to have each wheelchair tested with one or more specified commercial WTORS devices. This latter approach would add additional testing expense to the wheelchair industry, plus a great deal of confusion in the marketplace as to what combination of devices was tested as suitable for use. After considerable debate, the former position has been adopted, although more stringently in the ANSI/RESNA WC-19 standard than in the equivalent ISO 7176/19, in which it remains as an option.

A schematic representation of the surrogate wheelchair used in testingSpecifications for the Surrogate Wheelchair Used in the Dynamic Testing of Wheelchair Tiedown and Occupant Restraint Systems

In an effort to reduce the number of issues being initially addressed by the standard, it was decided to only include those wheelchair-seating devices that were provided by the wheelchair manufacturer. That is, work on third-party seating add-ons, for example, and other accessories was deferred and is now being addressed as a separate effort.

Finally, many of the principles being embedded in the design requirements of the standards were new concepts to the involved industries and their marketplaces. Therefore, the research team has been committed to developing guidelines that will assist designers in future designs, and clinicians and wheelchair users in the utilization of the standards. Application guidelines have been produced for the WTORS (J2249) standard, and those for the transport wheelchair standard (WC-19) are currently in process. A website ( http://www.rerc.upmc.edu/) has been developed by the RERC on Wheeled Mobility from which the latest working group draft standards and the J2249 application guideline can be downloaded. Others will be added as they become available.

Current Research Efforts
Current research efforts in support of improved wheelchair transport safety and related standards focus on those issues that were either deferred during the initiation of earlier work or have arisen during the development and implementation of the above standards. Four articles in this issue address several of these remaining issues.

One difficult question is, Who will bear the product liability if a second manufacturer's seat insert is added to the WC-19-tested wheelchair after production, which is a common clinical occurrence, especially in pediatric specialized seating? A way forward seems to be to have a seat component strength test that is acceptable to both industries. Research is now investigating how strong wheelchair seating components (seat, back, and attachment hardware) need to be in order to maintain a stable occupant support surface and hold the occupant in an appropriate position during a crash event so that the occupant restraint will function as intended. Again, the research is attempting to identify tests that will be valid, but not prohibitively expensive to implement for the involved industry as a test standard.

Obtaining proper occupant restraint fit when using a wheelchair as a motor vehicle seat is often difficult to attain with vehicle-mounted restraint systems. For example, rarely are the anchor points for the shoulder belt in the correct position on the vehicle wall to obtain proper body fit, especially for children. Offering both lap and shoulder belt for occupant restraint as an optional accessory on-board the wheelchair would allow customized body fit, and also give the user an increased degree of independence during transport. Research issues involve questions regarding the necessary strength of the seat back and wheelchair frame components to withstand the increased loads, and how the effectiveness of an integrated restraint system will be measured in a performance test standard.

As indicated, the four-point strap design is the worldwide industry standard for securing wheelchairs in motor vehicles. This approach evolved over many years as a practical solution within an environment in which there were no cross-industry communications or standards. Four-point strap securement has many inherent limitations, not the least of which is the limitation to transport independence of the wheelchair user. Today, we have a forum for cross-industry standards development, so alternate approaches to the wheelchair securement issue can be seriously considered. For example, research combined with prototype development has demonstrated the practicality of having a universal interface device (UID) that could be added as an optional accessory to the rear of any WC-19-designed wheelchair. Docking devices located within wheelchair stations in transport vehicles could be designed to dock with the standard UID. This approach opens the real possibility of independent wheelchair securement by the wheelchair occupant. That is, docking securement combined with integrated occupant restraint could free the wheelchair rider from any personal involvement with an attendant or the vehicle operator. Also, in all likelihood, this development would improve the level of safety and reduce the time required for wheelchair ingress and egress in public transit. Research work continues on this approach and early cross-industry standards development discussions have been initiated.

The Standards to Date
Space does not permit a detailed discourse on what has been implemented to date in the various industry standards related to wheelchair transport safety. As indicated, minor differences exist between the current U.S., Canadian and ISO versions. However, these differences are tending to narrow over time and are insignificant compared to the key requirements and test methods in which harmonization has been achieved. The following is an itemized summary of the key features contained in the standards now in effect or in the final stage of completion.

 

WHEELCHAIR TIEDOWN AND OCCUPANT RESTRAINTS (J2249, ISO 10542, Parts 1/2)

Scope:

Design Requirements:
Conforming WTORS must be designed to:

Conforming tiedowns must:

Conforming occupant restraints must:

Dynamic Strength:
When subjected to a 20 g, 30 mph (48 kph) crash pulse:

Identification, labeling, instruction and warning requirements:

 

WHEELCHAIRS FOR USE IN MOTOR VEHICLES (ANSI/RESNA WC-19, ISO 7176-19)

Scope:

Securement Points:

Pelvic Restraint:

Postural Supports:

Dynamic Strength:
When subjected to a 20 g, 30 mph (48 kph) crash pulse:

Identification, labeling, user instructions and warnings:

Future Work
Voluntary industry standards, once the most difficult first version has been successfully adopted and implemented, tend to take on a dynamic life of their own. Most national standards organizations, as well as the ISO, require a review and re-approval or revision of a standard every five years. This brings a new set of people to the table armed with the shortcomings discovered in having used the previous version and therefore anxious to implement changes warranted by practical experiences. It also allows for revisions that can include new innovations, technologies, and changes in clinical realities.

Much still remains to be done in the transport safety arena in terms of new standards development and related research. The following is only a brief overview of several of the key items that should lead to transport safety innovations in the near future.

As previously indicated, all add-on accessories, such as seating components, headrests, thoracic supports, knee blocks, trays, and anterior chest supports, have safety implications when used on a motor vehicle. Work in this area has just begun under the auspices of ISO 16840, led by Dr. Gina Bertocci.

Development of a docking securement standard is currently underway within the SAE and ISO working groups, led by Douglas Hobson. An early draft standard exists; however, agreement remains to be reached on the design of the UID. Parallel work is also taking place on a standard for clamping securement devices within ISO, led by Juan Dols of Spain.

In wheelchairs, the initial efforts have been focused exclusively on testing for a frontal impact on a forward-facing occupied wheelchair. Impacts, however, often occur from other directions, such as side and rear. Rollovers can also be the consequence of a vehicle collision. Standards development work, supported by ongoing laboratory research, needs to address these remaining impact directions, as is currently taking place in the vehicle industry. In the U.S., this new work will be organized within the ANSI/RESNA SOWHAT sub-committee, led by Larry Schneider. Dr. Schneider is also leading the preparation of the application guideline document on the recent ANSI/RESNA WC-19 standard.

The early work on totally integrated wheelchair occupant restraints offers many advantages, especially for school-age children and adults with limited upper body function. Currently, standards allow for the testing of such systems. Research and prototype development needs to demonstrate the design practicalities. As indicated by the article in this issue, the early stages of work are currently underway at the RERC on Wheeled Mobility, led by Dr. Gina Bertocci.

In conclusion, all standards development, to be successful, must be accompanied by an active dissemination and education program. Personnel from the RERC on Wheeled Mobility and others have actively hosted workshops and seminars on transport safety issues for consumers and clinicians for several years and will continue to do so. The RERC hosts a website on standards development that, in addition to posting the latest working group documents, also posts applications guidelines and slide presentations for downloading and use by others; see http://www.rerc.upmc.edu/.

Douglas A. Hobson, PhD


ACKNOWLEDGMENT

The Rehabilitation Engineering Research Center on Wheeled Mobility is supported by the National Institute on Disability and Rehabilitation Research, Department of Education, Washington, DC.

 

Standards:

  1. ANSI/RESNA-WC-19: Wheelchairs: Wheelchairs Used as Seats in Motor Vehicles, April 2000.
  2. SAE-J2249: Wheelchair Tiedown and Occupant Restraint Systems (WTORS) for Use in Motor Vehicles; Surface Vehicle Recommended Practice, Issued October 1996/Revised January 1999.
  3. SAE-J2252: Surrogate Wheelchair Drawing Package and Maintenance Manual, 2000.
  4. ISO /DIS 10542-1: Technical Systems and Aids for Disabled and Handicapped Persons--Wheelchair Tiedowns and Occupant Restraint Systems--Part 1: Requirements and Test Methods for All Systems, Draft International Standard, 1999.
  5. ISO /DIS 10542-2: Technical Systems and Aids for Disabled and Handicapped Persons--Wheelchair Tiedowns and Occupant Restraint Systems--Part 2: Four Point Strap Type Tiedown Systems, Draft International Standard 1999.
  6. ISO10542-3: Technical Systems and Aids for Disabled and Handicapped Persons--Wheelchair Tiedowns and Occupant Restraint Systems--Part 3: Docking Tiedown Systems, Working Draft, 2000.
  7. ISO 10542-4: Technical Systems and Aids for Disabled and Handicapped Persons--Wheelchair Tiedowns and Occupant Restraint Systems--Part 4: Clamping Systems, Working Draft, 2000.
  8. ISO /AWI 16840-4: Wheelchair Seating: Seating for Use on Motor Vehicles, Approved Work Item, 1999.
  9. ISO/DIS 7176-19 Wheelchairs--Part 19: Wheeled Mobility Devices for Use in Motor Vehicles, Draft International Standard, 2000.

Resources:

 

Go to TOP.

 
Links to PDF Version of this article.

Last Updated Monday, November 24, 2008 11:37 AM