SP-5: Investigation, Development and Evaluation of Wheelchair Integrated Restraint Systems for Adults and Children

Importance of the problem

Description of the need and target population

Individuals with limited mobility and requiring assistance during transfers, often use wheeled mobility devices (manual wheelchair, power wheelchair, or scooter) as motor vehicle seats during transit in motor vehicles. Para-transit vans, public busses and privately owned vehicles transport individuals using wheelchairs on a daily basis providing them with access to education, work or recreational activities. These types of transit vehicles are often equipped with wheelchair tiedown and occupant restraint systems. Strap and docking type wheelchair securement systems fasten wheelchairs to the vehicle floor during transport. Upper torso and pelvic-restraint systems to protect wheelchair occupants from injury during motor vehicle impact are typically attached to the motor vehicle structure. The voluntary ANSI/RESNA WC19 (ANSI/RESNA, 2000) standard requires wheelchair integrated pelvic restraints for compliance (phase-in period of two years). However, current practice consists of wheelchair occupant restraint systems (WORS) attached to a fixed location on the vehicle structure. Studies have shown that vehicle mounted occupant restraint systems (VMRS), consisting of upper torso and pelvic restraints, often result in poor belt-fit and decreased occupant protection when used for a varying occupant population who utilize various wheelchair sizes and designs (Aibe, Watanabe et al., 1982; Bertocci, Digges et al., 1996; Bertocci, 1997; van Roosmalen, Bertocci et al., 1998; Bertocci and Evans, 2000; Bunai, Nagai et al., 2001).

Extensive research has been done in the automotive industry to study the effect of restraint system design on occupants. It was found that poorly positioned occupant restraints pose an increased risk of head, chest and abdominal injuries during impact events (Cocke and Meyer, 1963; Epstein, Epstein et al., 1978; Horsch and Hering, 1989; Miller, 1989; Partyka, 1990; Horsch, Viano et al., 1991). Additionally, discomfort of occupant restraints has been found to be an important factor contributing to 'non belt usage' (NHTSA, 1997; NHTSA, 1999). Results from investigations of individuals using their wheelchairs as motor vehicle seats during transportation in para-transit vehicles and public busses, affirm the need for improved wheelchair occupant restraint systems that are safe, comfortable, easy and independent to use (Sprigle, Morris et al., 1994; Linden, Kamper et al., 1996; Bunai, Nagai et al., 2001; van Roosmalen, Bertocci et al., 2001; van Roosmalen, Bertocci et al., Accepted for publication April 2001).

Research in the automotive industry has found improved occupant crash protection and user comfort with seat integrated occupant restraint systems (Cremer, 1983; Haberl, Ritzl et al., 1989; Blaisdell, Levitt et al., 1993; Cole and Johnson Controls, 1993; Lynch, 1995). Integrated restraint technology applied to wheelchairs may therefore have the effect of improved occupant crash protection, usability and comfort. In a preliminary study conducted at the University of Pittsburgh, a concept wheelchair integrated occupant restraint system (WIRS) featuring a wheelchair mounted upper torso and pelvic restraint was constructed and evaluated using quasi-static and dynamic test methods. Frontal sled impact testing using a 50th percentile male Anthropomorphic Test Dummy, proved WIRS crash safety compliance with safety standards (van Roosmalen and Bertocci, 1999; van Roosmalen and Bertocci, 2000; van Roosmalen and Bertocci, 2001; van Roosmalen, Bertocci et al., Submitted Feb. 2001). A computer simulation model was built and validated based on frontal sled impact test data (van Roosmalen, Bertocci et al., 2001), and a sensitivity analysis was conducted on wheelchair seating system and occupant restraint parameters using this computer simulation model. This study and previously conducted studies in the automotive industry confirmed that multiple parameters such as reduced restraint slack and the inclusion of restraint pretensioners and restraint load-limiters reduce restraint loads and occupant injury risk (Ruter and Hontschik, 1979; Woodson, Selby et al., 1980; Haberl, Ritzl et al., 1989; Foret Bruno, Trosseille et al., 1998; van Roosmalen, 2001). Besides restraint characteristics, wheelchair seating system design parameters such as seat stiffness, seat- to back joint stiffness and seat back recline angle were also found to affect wheelchair seat surface loads and occupant injury measures (Dolan and Oilar, 1986; Strother and James, 1987; Viano, 1992; Blaisdell, Levitt et al., 1993; Saczalski, Syson et al., 1993; Benson, Smith et al., 1996; NHTSA, 1998; Bertocci and Szobota, 2000; Souza and Bertocci, 2001; van Roosmalen, 2001).

In summary, previous studies suggest that WIRS may provide wheelchair occupants with improved safety, comfort, independence and ease of use when restraining themselves during transport in motor vehicles. Further research is also needed to study the crashworthiness of wheelchair structures when integrating occupant restraint systems in wheelchair seats. Additional research is needed to further study the potential of WIRS concepts applied to current wheelchair designs and to further evaluate WIRS occupant protection features, usability, user comfort and esthetics.

Beneficial impact on target population, including service providers

WIRS have the potential to beneficially impact individuals who are unable to transfer from their wheelchairs into motor vehicle seats and who use motor vehicles for daily transport for health care, work or leisure. This improved type of occupant restraint will benefit individuals who are currently restrained using fixed vehicle mounted restraints that fit poorly, are time consuming to engage and require an attendant for use. When combined with automated wheelchair securement, many individuals will likely be able to independently restrain themselves and secure their wheelchair for safe transport in motor vehicles. Other constituents benefiting from WIRS are transport organizations who must provide operator assistance to engage occupant restraints.

Responsiveness to priority

These tasks respond to the announced priority “To investigate, develop and evaluate integrated occupant restraint systems that are independent of the vehicle and easy for wheelchair-seated occupants to operate”.

Overall objectives

The overall objectives of tasks SP-5a, SP-5b and SP-5c include the following.

  1. Determine the need for improved occupant restraint systems from manufacturers, clinicians and caregivers.
  2. Develop a set of detailed design guidelines and technical requirements to assist in future development and evaluation of wheelchair integrated occupant restraint systems.
  3. Develop and utilize a surrogate WIRS prototype to investigate the effects of various key restraint system design parameters.
  4. Develop standard test procedures to evaluate occupant protection features for adult and pediatric users. Develop and materialize adult and pediatric WIRS concepts.
  5. Construct prototype WIRS for adult and pediatric users. Evaluate WIRS prototypes through usability studies and dynamic sled impact testing.


  1. Aibe, T., Watanabe, K., Okamoto, T. and Nakamori, T. (1982). “Influence of occupant seating posture and size on head and chest injuries in frontal collision.” SAE.
  2. ANSI/RESNA (2000). Wheelchairs used as seats in motor vehicles. Arlington, VA, RESNA.
  3. Benson, B., Smith, G., Kent, R. and Monson, C. (1996). “Effect of seat stiffness in out-of-position occupant response in rear end collisions.” SAE.
  4. Bertocci, G. and Szobota, S. (2000). Effect of wheelchair seating stiffness on occupant crash kinematics and submarining risk using computer simulation. RESNA, Orlando, FL, RESNA Press.
  5. Bertocci, G. E. (1997). The Influence of securement point and occupant restraint anchor location on wheelchair frontal crash safety. Bioengineering. Pittsburgh, University of Pittsburgh.
  6. Bertocci, G. E., Digges, K. & Hobson, D. A. (1996). “Shoulder belt anchor location influences on wheelchair occupant crash protection.” Journal of Rehab Research and Development 33(3): 279-289.
  7. Bertocci, G. E. and Evans, J. (2000). “Injury risk assessment of wheelchair occupant restraint systems in a frontal crash: a case for integrated restraints.” Journal of Rehabilitation Research and Development 37(5): 573-589.
  8. Blaisdell, D. M., Levitt, A. E. and Varat, M. S. (1993). Automotive seat design concepts for occupant protection. Society of Automotive Engineers, SAE.
  9. Bunai, Y., Nagai, A., Nakamura, I. & Ohya, I. (2001). “Blunt pancreatic trauma by a wheelchair user restraint system during a traffic accident.” Journal of Forensic Science 46(4): 965-968.
  10. Cocke, W. and Meyer, K. (1963). “Splenic rupture due to improper placement of automotive safety belt.” JAMA 183: 193.
  11. Cole, J. H. and Johnson Controls (1993). Developing a cost effective integrated structural seat. Society of Automotive Engineers.
  12. Cremer, H. P. (1983). Seat integrated safety belt. Society of Automotive Engineers (SAE).
  13. Dolan, M. and Oilar, J. (1986). “How Seat Design Characteristics Affect Impact Injury Criteria.” SAE Paper No. 860638.
  14. Epstein, B., Epstein, J. and Jones, M. (1978). “Lap-sash three point seat belt fractures of the cervical spine.” Spine 3: 189-193.
  15. Foret Bruno, J.-Y., Trosseille, X., Le Coz, J.-Y., Bendjellal, F., Steyer, C., Phalempin, T., Villeforceix, D., Dandres, P. and Got, C. (1998). Thoracic injury risk in frontal car crashes with occupant restrained with belt load limiter. Society of Automotive Engineers (SAE).
  16. Haberl, J., Ritzl, F. and Eichinger, S. (1989). The effect of fully seat-integrated front seat belt systems on vehicle occupants in frontal crashes. ESV-Conference Goteborg, Goteborg, Bayerische Motoren Werke AG, Vehicle Safety, Munich, Germany.
  17. Horsch, J. and Hering, W. (1989). A kinematic analysis of lap belt submarining for test dummies, SAE.
  18. Horsch, J., Viano, D. and Mertz, H. (1991). Thoracic injury assessment of belt restraint systems based on Hybrid III chest compression, SAE.
  19. Linden, M. A., Kamper, D. G., Reger, S. I. and Adams, T. C. (1996). Transportation needs: Survey of individuals with disabilities. RESNA annual conference, RESNA Press.
  20. Lynch, T. (1995). “Integrated seat adds safety, design convenience.” Design News 43(October).
  21. Miller, M. (1989). “The biomechanics response of the lower abdomen to belt restraint loading.” Journal of Trauma 29(11).
  22. NHTSA (1997). Buckle up America, Department of Transportation. 1997.
  23. NHTSA (1999). Advanced integrated structural seat, EASI Eng. & Johnson Controls Inc.
  24. NHTSA, M., L. (1998). Determination of moment deflection characteristics of auto seat backs. Washington, DC, NTHSA.
  25. Partyka (1990). “Comparison of belt effectiveness in preventing chest, head and face injuries in front and rear impacts.”
  26. Ruter, G. and Hontschik, H. (1979). Protection of occupants of commercial vehicles by integrated seat/belt systems. 23rd Stapp Car Crash Conference, San Diego, California, USA, Society of Automotive Engineers, Inc., Warrendale, Pennsylvania, USA.
  27. Saczalski, K. J., Syson, S. R., Hille, R. A. and Pozzi, M. C. (1993). Field accident evaluations and experimental study of seat back performance relative to rear-impact occupant protection. SAE, SAE.
  28. Souza, A. L. and Bertocci, G. E. (2001). The effects of wheelchair seating system energy absorption on occupant submarining risk in a frontal impact using computer simulation. RESNA annual conference, Reno, RESNA Press.
  29. Sprigle, S., Morris, B., Nowacek, G. and Karg, P. (1994). “Assessment of adaptive transportation technology: a survey of users and equipment vendors.” Assistive Technology 6: 111-119.
  30. Strother, C. E. and James, M. B. (1987). Evaluation of seat back strength and seat belt effectiveness in rear impact, SAE: 225-243.
  31. van Roosmalen, L. (2001). Wheelchair integrated occupant restraint system feasibility in frontal impact. Rehabilitation Science and Technology, Dissertation. Pittsburgh, University of Pittsburgh.
  32. van Roosmalen, L. and Bertocci, G. E. (1999). Adaptation of integrated restraint technology for use in wheelchair transportation. IEEE EMBS, Atlanta, Georgia.
  33. van Roosmalen, L. and Bertocci, G. E. (2000). Evaluation of the Seat Belt Anchorage Strength of a Prototype Wheelchair Integrated Occupant Restraint System. RESNA annual conference, Orlando, FL, RESNA Press.
  34. van Roosmalen, L. and Bertocci, G. E. (2001). The effect of a wheelchair integrated occupant restraint system on wheelchair tie-down and occupant restraint design characteristics. RESNA annual conference, Reno, RESNA Press.
  35. van Roosmalen, L., Bertocci, G. E., Ha, D. and Karg, P. (Submitted Feb. 2001). “Wheelchair integrated occupant restraints: Feasibility in frontal impact.” Medical Engineering & Physics.
  36. van Roosmalen, L., Bertocci, G. E., Hobson, D. A. and Karg, P. (2001). Usability and satisfaction of wheelchair occupant restraint systems used during motor vehicle transport. RESNA annual conference, Reno, RESNA Press.
  37. van Roosmalen, L., Bertocci, G. E., Hobson, D. A. and Karg, P. (Accepted for publication April 2001). “Preliminary evaluation of wheelchair occupant restraint system usage in motor vehicles.” Journal of Rehabilitation Research and Development.
  38. van Roosmalen, L., Bertocci, G. E., Karg, P. and Young, T. (1998). Belt fit evaluation of fixed vehicle mounted shoulder restraint anchors across mixed occupant populations. RESNA annual conference, Minneapolis, MN, RESNA Press.
  39. van Roosmalen, L., Bertocci, G. E. and Leary, A. (2001). Computer simulation validation of a wheelchair mounted occupant restraint system under frontal impact. RESNA annual conference, Reno, RESNA Press.
  40. Viano, D. (1992). “Influence of seat back angle on occupant dynamics in simulated rear-end impacts.” Society of Automotive Engineers (SAE).
  41. Woodson, W., Selby, P. and Coburn, R. (1980). Comfort and convenience specifications for safety belts: Shoulder belt fit, pressure, and pullout forces, Man Factors, Inc.

5 year report June 1, 2006

A paper survey and web survey were conducted and a total of 127 wheelchair users who use their wheelchair as a motor vehicle seat were surveyed. Results were recorded in a File Maker Pro document and conclusions of the study are currently published in the Journal of Assistive Technology.

A focus group study was also conducted at the 2002 Annual RESNA Conference in Minneapolis. Wheelchair/seating manufacturers (Sunrise Medical/Invacare), occupant restraint manufacturers (Sure-Lok), researchers (PITT/UMTRI), clinicians, transit organizations and wheelchair user advocates participated in the 3 hour focus group.

A usability study was held to obtain issues and design characteristics of a wheelchair integrated occupant restraint system for adult wheelchair users. An adjustable frame was developed and equipped with a digital measuring instrument (FARO arm). Wheelchair and occupant data was collected from a variety of 10 wheelchairs and adult wheelchair users. Data acquisition with Excel and digital video recorded wheelchair and occupant measurements as well as seat belt design issues. Data from the usability study has been published in two journals, Applied Ergonomics and Journal of Assistive Technology.

A network with wheelchair manufacturers and seat belt manufacturers has been established to assist with manufacturability of prototypes. A design of a user friendly and safe pelvic restraint system will be developed to work with the existing on board shoulder belt.

Based on user testing and input from wheelchair users via the world wide web, information was gathered into a Quality Function Deployment matrix. This matrix has been communicated to wheelchair users and clinicians at RESNA. The QFD and more detailed design guidelines are now in the process of being communicated to constituents in the form of publications and online guidelines.

Several seat integrated lap belt concepts were been developed and one was tested in an ergonomic study with actual wheelchair users. Eight users gave comments on the lap belt concept and an improved concept us currently being manufacturerd by an Industry partner.

As part of SP5, one seat integrated lap belt concept (concept 1) will be prototyped and evaluated. An other innovative concept will be developed using additional funding from the National Innovators and Inventors Allience.

Concept 1: An integrated pelvic belt with various features to make the belt easier to use for people with limited upper extremity function. An attachment point for a vehicle mounted shoulder belt portion is included.

User testing showed that the restraint is easier to use than existing buckle type restraints. Furthermore, the restraint seems comfortable for a wide range of users. After the usability studies on a first prototype a second prototype is being developed for sled testing purposes. Results are expected in the summer of 2006. There is Industry interest in this pelvic restraint and it is expected that a commercial product for use on wheelchairs will be launched in 2007.

Concept 2: A rigid type integrated pelvic belt that can be buckled up with one easy motion.

A mockup of this idea was developed and preliminary user input shows that this concept will be easy to use for people with limited upper extremity function. Additional funds were obtained from NCIIA to investigate the potential of this design. A prototype is expected to be completed and crash tested by the Fall of 2006.

Based on the design guidelines used to conceive the above concepts a technical guideline on “how to design wheelchair integrated restraints for adults” is under development and expected to be completed in the Fall of 2006.

Pediatric Restraint:

This project investigated the feasibility and design criteria for wheelchair-integrated (i.e., wheelchair-anchored) belt-type occupant restraint systems for pediatric wheelchair users, with special emphasis on five-point harness systems for children under 23 kg (50 lb) mass.  The initial portion of the project defined design guidelines for integrated restraint harnesses using information from the federal motor vehicle safety standard for child restraint systems (FMVSS 213), from well-established principles of occupant restraint, from ease-of-use issues for child restraint systems based on field observations, and from studies of automotive-seated child anthropometry. 

The draft version of these design guidelines was used to implement five-point harnesses obtained from current FVMSS 213-compliant child safety seats on current pediatric commercial wheelchair products.  The prototypes were frontal-impact tested to evaluate the crashworthiness of each prototype based on established performance criteria from FMVSS 213.  The tests also provided quantitative information on forces applied by harness shoulder belts to the wheelchair seatback for use wheelchair manufacturers in designing their pediatric products for use with fully integrated restraint systems. 

Based on the information collected during the process of developing and testing these prototypes, the design guidelines were revised and improved, to include strength requirements and issues specific to wheelchair encountered during the prototyping process.  These guidelines are now being used to augment ANSI/RESNA WC19 with design and performance criteria for wheelchair-integrated, five-point harnesses for wheelchairs used by children under 23 kg (50 lb).  

Last updated: March 18, 2006