SP-2a: Biomechanics of Injury to Wheelchair-Seated Occupants in Rear Impacts

Task co-leaders: Lawrence Schneider, PhD and Miriam Manary, MSE

Co-investigator: Gina Bertocci, PhD



Other participants: University of Michigan Engineering Graduate Student (student), Jean Marc Girardin of Q’Straint (manufacturer), Ruth Lytle of Everest and Jennings (manufacturer), Steve Linquist of Sunrise Medical Mobility Systems (manufacturer), Jim Swinehart of Metalcraft Industries (manufacturer), Tom Novotny of AES (manufacturer), University of Michigan Health System Physical Therapists and Patients, (clinicians and consumers) and RESNA SOWHAT members (researchers, clinicians, consumers, students, and industry representatives).

Duration/Staging of task: This is a 30-month research task that will be conducted primarily in months 1-30 of the 60 month RERC cycle.

Research objectives

This task operates on the hypothesis that rear-impact protection can be significantly improved for wheelchair-seated travelers by understanding and applying the established concepts of rear impact protection developed for the automotive environment. The research and development plan to improve occupant protection for forward-facing wheelchair-seated occupants in rear-end impacts involves several tasks with individual objectives. These include:

  1. conduct a thorough review of the biomechanical literature and existing federal safety standards relevant to rear-impact crashes and summarize and document the results as they may be relevant to developing test methods, and design and performance requirements for devices and equipment used by wheelchair-seated occupants.
  2. using input from Task 1c to determine an appropriate impact pulse, conduct simulated rear-end impact tests to evaluate the performance of different types of wheelchairs and WTORS that comply with the frontal crash requirements of SAE J2249 and ANSI/RESNA WC/19 to assess the problem areas and needs.
  3. based on the results of (b), develop appropriate modifications to test methods and test instrumentation for conducting rear-impact sled impact tests.
  4. modify existing computer models used for frontal-impact wheelchair/occupant simulations for use in rear-impact simulations, and validate models using results from sled impact tests conducted in (b) and (c),
  5. use sled impact testing and computer simulations to study rear-impact protection issues for wheelchair-seated occupants and to establish performance criteria for wheelchairs and vehicle-installed backrests and headrests.
  6. use the existing wheelchair dimensional database at University of Pittsburgh, along with additional measurements of wheelchair provided by manufacturers, to examine the geometric constraints and problems of providing effective vehicle-installed head and back supports for wheelchair-seated occupants,
  7. use the results from (a) through (e) to establish a set of test methodologies and associated performance criteria for inclusion in future wheelchair and WTORS standards,
  8. in conjunction with collaborating manufacturers, develop prototype wheelchair and vehicle-installed backrests and headrests that comply with the criteria established in (f).

Anticipated outcomes

The overall goal of this activity is to reduce rear-impact injury for people who travel in a motor vehicle while seated in a wheelchair. This task will result in:

  1. a thorough compilation and analysis of existing literature on rear impact,
  2. an impact pulse appropriate for rear impact testing and simulation,
  3. an evaluation of current wheelchair and wheelchair tiedown designs as to their appropriateness for rear-impact protection,
  4. new test methods and instrumentation requirements for assessment of rear-impact risks
  5. new computer models that simulate rear-impacts of wheelchair–seated travelers,
  6. an understanding of the geometric constraints and challenges of providing vehicle –mounted head and back support systems,
  7. rear impact performance criteria and draft standards, and prototype hardware and/or design requirements that can aid manufacturers in the creation of products with improved rear-impact protection.

References

Aldman, B., An Analytical Approach to the Impact Biomechanics of the Head and Neck. American Association for Automotive Medicine, p 439-454, 1986.

Bertocci, G, Karg, P, Hobson, D. Wheeled Mobility Device Database for Transportation Safety Research and Standards, Assistive Technology, 1997. Vol 9.2: p. 102-115.

Boström O., Bohman K., Håland Y., Kullgren A., Krafft M., New AIS1 Neck Injury Criteria Candidates for Frontal Collisions, IRCOBI Conference, London, England, 2000

Boström O., Svensson M., Aldman B. et al. A New Injury Criterion Candidate-Based on Injury Findings in the Cervical Spinal Ganglia after Experimental Sagittal Whiplash., Proceedings International IRCOBI Conference, pp. 123-136, 1996

Deng, Y.C. Anthropomorphic Dummy Neck Modeling and Injury Considerations. Accident Analysis and Prevention. Vol 21 no 1, pp 85-100, 1989

Foret-Bruno, J.Y. Dauvilliers, F., Tarriere, C. Influence of the Seat and Headrest stiffness on the Risk of Cervical Injuries in Rear Impact., Proceedings of 13th EVS Conference, Paper 91-S8-W-19 NHTSA, Washington, DC, 1991.

Garrett, W.E., Seaber, A.V., Best, T.M., Glisson, R.R., Nikolaou, P.K., and Taylor, D.

C., Muscle Strain Injury: Basic Science and Clinical Application, 43rd Annual Meeting of Orthopedic Research Society, 1997.

Gurdijan, Neckache and Backache Due to Degenerative and/or Traumatic Musculoskeletal Processes: a By-Product of Modern Culture, Neckache and Backache, C.C. Thomas, Springfield IL, pp 3-23, 1970.

Kleinberger, M., Sun, E., Eppinger, R., Kuppa S., Saul R. Development of Improved Injury Criteria for the Assessment of Advanced Automotive Restraint System. NHTSA Docket 98-4405-9. US Dept. of Transportation. Washington, D.C, 1998

Kleinberger, M., Sun, E., Saunders, J., and Zhou, Z., Effects of Head Restraint Position on Neck Injury in Rear Impact. Whiplash-Associated Disorders World Congress, 1999.

Langweider K., Hell W., Schick S., Muser M., Waltz F., Zellmer H. Evolution of Dynamic Seat Test Standard Proposal for a Better Protection after Rear-End Impact, International IRCOBI Conference, Montpellier, France, 2000.

MacNab, I., Whiplash Injuries of the Neck. American Association for Automotive Medicine, 1965.

McConnell, W.E., Howard, R.P., Guzman, H.M., Bomar, J.B., Raddin, J.H. Benedict J.V., Smith L.H. and Hatsell, C.P. Analysis of Human Test Subject Responses to Low Velocity Rear end Impact. Paper 930889. Society of Automotive Engineers, Warrendale, PA, 1993.

Melvin, J.W. and McElhaney, J.H., Occupant Protection in Rear-end Collisions, SAE Technical Paper Number 720033, Society of Automotive Engineers, Warrendale, PA., 1972.

Mertz, H.J. and Patrick, L.M. Investigations of the Kinematics and Kinetics of Whiplash, SAE Transactions, Vol 76, paper 670919, 1967

NHTSA, Standardized Child Passenger Safety Training Program, DOT, Washington, DC, 2000.

Nygren, A., Gustafsson, H. and Tingvall, C. Effect of Different Types of Headrest in Rear-End Collisions. 10th International Conference on Experimental Safety Vehicles, p 85-90, NHTSA, USA 1985.

Ono, K., Kaneoka K., Wittek, a., Kajzer, J., Cervical Injury mechanism Based on the analysis of Human Cervical Vertebral Motion and Head-Neck-Torso Kinematics During Low Speed Rear Impacts, Proceeding of the 41st Stapp Car Crash Conference, 1997.

Panjabi M., Wang J., Delson N. Neck Injury Criterion Based on Intervertebral Motions and its Evaluation using an Instrumented Neck Dummy, Proceedings of IRCOBI Conference, Sitges, Spain 1999

Portnoy, et al, Intracranial Pressure and Head Acceleration During Whiplash. Stapp Car Crash Conference SAE paper 700900, SAE 1970

Seeman, M.R., Muzzy, W.H., and Lustick, L.S., Comparison of Human and Hybrid III Head and Neck Response. Proceedings of the 30th Stapp Car Crash Conference, paper 861892, pp 291-312, 1986.

Severy, D.M., Mathewson, J.H. and Bechtol, C.O., Controlled Automobile Rear-end Collisions, an Investigation of Related Engineering and Medical Phenomena. Canadian Services Medical Journal VII, 727-759, 1955.

Svensson M., Lövsund P. A, Dummy for Rear-End Collisions – Development and validation of a new dummy-neck., Doctoral thesis, Department of Injury Prevention, Chalmers University of Technology, S-412 96 Göteborg, Sweden, 1992

Svensson, M.Y., Lövsund, P., Haland, Y., Larsson, S. The Influences of the Seatback and Head Restraint Properties on the Head-Neck Motion During Rear-Impact, IRCOBI, 1993.

Svensson M., Boström O., Davidsson J., Hansson H., Håland Y., Lövsund P., Suneson A., Säljö A. Neck Injuries in Car Collisions-A Review Covering a Possible Injury Mechanism and the Development of a New Rear-Impact Dummy. Accident Analysis and Prevention 32, pp. 167-175, 2000

Tencer, A., Mirza, S., Martin, D., Goodwin, V., Sackett, R., and Schaefer, J., Development of a Retro-fit Anti Whiplash Seat Cushion Based on Studies of Drivers and Human Volunteers, 9th Injury Prevention Through Biomechanics Symposium, p 39-45, 1999.

TES Limited, Accidents Involving Seat Back Failures, Report C1322/2, Transport Canada, Ottawa Ontario, 1989.

Thunnisen J., van Ratingen., Beusenberg M., Janssen E. A, Dummy Neck For Low Severity Rear Impacts. Fifteenth International Technical Conference on the Enhanced Safety of Vehicles, World Congress Centre, Melbourne, Australia 1996.

Traffic Safety Facts 1998, NHTSA, Washington DC, 1999.

Viano, D.C., Influence of Seatback Angle on Occupant Dynamics in Simulated Rear-End Impacts. Proceedings of the 36th Stapp Car Crash Conference, paper 922521, p 157-164, 1992.

Viano, D.C., Restraint of a Belted or Unbelted Occupant by the Seat in Rear-End Impacts. Proceedings of the 36th Stapp Car Crash Conference, paper 922522, p 164-177, 1992.

Wismans J. and Kroonenberg A.J. European Research in Whiplash Injury Prevention. Traffic Safety and Auto Engineering Stream, WAD World Congress, 7-11 Feb., Vancouver, Canada, 1999

Yang, K.H., and Begeman, P.C., A Proposed Role for Facet Joints in Neck Pain in Low to Moderate Speed Rear End Impacts Part I: Biomechanics,. 6th Injury Prevention Through Biomechanics Symposium, p 59-63, 1996.

Yoganandan, N., Pintar, F.A., Cusick, J.F., Sun, E., and Eppinger, R., Whiplash Injury Mechanisms. Whiplash ’98 Symposium, p 23, 1998.


Progress Report June 1, 2003

This task is investigating the safety of forward-facing wheelchair-seated motor-vehicle occupants in rear-impact crash conditions and is exploring injury-reduction strategies. The project R& D activities include: 1) evaluating how current transit wheelchairs (i.e., those that comply with the current frontal impact standard, ANSI/RESNA WC19) perform under rear impact conditions, 2) reviewing and synthesizing the relevant scientific literature, 3) performing rear-impact tests with an instrumented wheelchair seatback to determine seatback strength requirements and relationships between seatback stiffness and neck loads, and 4) performing a study of wheelchair dimensions and designs relative to implementation of vehicle-anchored seatback and headrest supports.

Dynamic testing has shown that many current wheelchair designs, including those that perform satisfactorily under 30-mph frontal-impact loading, do not provide an adequate level of seatback strength and occupant protection under 18-mph, 14-g rear-impact loading. Comprehensive seatback failure is a common outcome and such failures result in the wheelchair occupant being essentially unrestrained from moving rearward into contact with vehicle interior components and/or other vehicle occupants. One notable exception is a stroller-type wheelchair that maintained a midsize male crash dummy in a seated position with head support during the rear impact test.

The literature review has been completed and covers all areas related to rear-impact injuries, including: 1) injury patterns, injury mechanisms, and injury criteria, 2) appropriate crash severities for rear-impact testing, 3) different anthropomorphic test devices (ATDs) for use in rear-impact testing, 4) federal and international safety standards related to rear-impact protection, and 5) restraint design for rear-impact protection. Additional analyses of the NASS (National Automotive Sampling System) database were conducted to determine the distribution of rear-impact crash severities and the results are being used to further establish the most appropriate rear-impact crash pulse for use in future dynamic testing and standards development related to transportation of wheelchair-seated occupants. In particular, an effort is being made to use the NASS analysis to compare the distribution of rear-impact crash severities for all passenger cars to the distribution of crash severities to passenger vehicles most frequently used for private vehicle transportation of wheelchair-seated passengers, such as minivans and vans.

Sled impact testing of a load-cell instrumented seatback mounted on the new surrogate wheelchair base is being used to quantify seatback strength requirements in relation to seatback deflection properties. In addition, the relationship between ATD loads and excursions will be evaluated with the goal of determining optimum backrest performance for both occupant retention and injury reduction. Results of sled-impact testing will be supplemented by performing computer simulations of wheelchairs and occupants in rear impact loading. This will be accomplished by configuring MADYMO, a model frequently used by the automotive industry for crash simulations, to represent typical wheelchair structural designs and occupant loading.

A compilation of wheelchair frame and seatback geometry is planned to help formulate design guidelines for vehicle-mounted head and back supports. These data, along with the test results and computer simulations will be used to assist WTORS manufacturers in developing and testing prototype backrest and headrest components that offer improved occupant protection under rear-impact conditions.

The results of research and testing in Task 2a will used to establish design specifications and performance criteria for wheelchairs and WTORS that will provide improved protection to forward-facing wheelchair users in rear impacts. These specifications and criteria, and the associated test methods, will be used to augment existing transit wheelchair and WTORS standards for frontal crash protection.


Progress Report June 1, 2004

This task focuses on crash safety of forward-facing, wheelchair-seated, motor-vehicle occupants in rear-impacts and is exploring injury-reduction strategies. The project activities include:

  1. evaluating how current transit wheelchairs (i.e., those that comply with the current frontal impact standard, ANSI/RESNA WC19) perform under rear impact conditions,
  2. reviewing and synthesizing the relevant scientific literature,
  3. performing rear-impact tests with an instrumented wheelchair seatback to determine seatback strength requirements and relationships between seatback stiffness and neck loads, and
  4. performing a study of wheelchair dimensions and designs relative to implementation of vehicle-anchored seatback and headrest supports.

The work this year has focused on items 3 and 4 in the list above.

A sled impact test series of a load-cell instrumented seatback (ISB) mounted on the new surrogate wheelchair base was completed and the result presented in a RESNA paper in June 2004. The ISB was used to quantify seatback strength requirements in relation to seatback deflection properties. In addition, the relationship between ATD loads and excursions will be evaluated with the goal of determining optimum backrest performance for both occupant retention and injury reduction. Results of sled-impact testing are being supplemented by MADYMO models of wheelchairs and occupants in rear impact loading that have been validated with the ISB test series.

A survey of wheelchair frame and seatback geometry is nearly complete with 99 of 100 wheelchairs already measured. The data are being analyzed to formulate design guidelines for vehicle-mounted head and back supports and evaluate existing back support designs for compatibility with current wheelchairs. These data, along with the test results and computer simulations will be used to assist WTORS manufacturers in developing and testing prototype backrest and headrest components that offer improved occupant protection under rear-impact conditions.

The results of research and testing in Task 2a will be used to establish design specifications and performance criteria for wheelchairs and WTORS that will provide insight into improved protection to forward-facing wheelchair users in rear impacts. These specifications and criteria, and the associated test methods, will be used to augment existing transit wheelchair and WTORS standards.


Progress Report June 1, 2005

This task focuses on crash safety of forward-facing, wheelchair-seated, motor-vehicle occupants in rear-impacts and is exploring injury-reduction strategies. The project activities include: 1) evaluating how current transit wheelchairs (i.e., those that comply with the current frontal impact standard, ANSI/RESNA WC19) perform under rear impact conditions, 2) reviewing and synthesizing the relevant scientific literature, 3) performing rear-impact tests with an instrumented wheelchair seatback to determine seatback strength requirements and relationships between seatback stiffness and neck loads, and 4) performing a study of wheelchair dimensions and designs relative to implementation of vehicle-anchored seatback and headrest supports. The work this year has focused on items 3 and 4 in the list above.

A sled impact test series of a load-cell instrumented seatback (ISB) mounted on the new surrogate wheelchair base was completed and the result presented in a RESNA paper in June 2004. The ISB was used to quantify seatback strength requirements in relation to seatback deflection properties. In addition, the relationship between ATD loads and excursions will be evaluated with the goal of determining optimum backrest performance for both occupant retention and injury reduction. Results of sled-impact testing are being supplemented by MADYMO models of wheelchairs and occupants in rear impact loading that have been validated with the ISB test series.

A survey of wheelchair frame and seatback geometry is nearly complete with 99 of 100 wheelchairs already measured. The data are being analyzed to formulate design guidelines for vehicle-mounted head and back supports and evaluate existing back support designs for compatibility with current wheelchairs. These data, along with the test results and computer simulations will be used to assist WTORS manufacturers in developing and testing prototype backrest and headrest components that offer improved occupant protection under rear-impact conditions.

The results of research and testing in Task 2a will be used to establish design specifications and performance criteria for wheelchairs and WTORS that will provide insight into improved protection to forward-facing wheelchair users in rear impacts. These specifications and criteria, and the associated test methods, will be used to augment existing transit wheelchair and WTORS standards.

Last updated: August 30, 2005


5 year report June 1, 2006

This task investigated the safety of forward-facing wheelchair-seated,  motor-vehicle occupants in rear-impact crash conditions and explored injury-reduction strategies.  The project activities include: 1) sled-test evaluations of how WC19 wheelchairs (i.e., those that comply with the current frontal impact standard, ANSI/RESNA WC19) perform under rear-impact conditions, 2) review and synthesis of the relevant scientific literature,  3) rear-impact tests with an instrumented wheelchair seatback to determine seatback strength requirements and relationships between seatback stiffness and ATD loads, and 4) a study of wheelchair dimensions and designs relative to implementation of vehicle-anchored seatback and headrest supports.

The rear-impact tests of six WC19 wheelchairs showed that many current wheelchair designs, including those that perform satisfactorily under 30-mph frontal-impact loading, do not provide an adequate level of seatback strength and occupant protection under 18-mph, 14-g rear-impact loading.  Comprehensive seatback failure was a common outcome and such failures resulted in the wheelchair occupant being essentially unrestrained from moving rearward into contact with vehicle interior components and/or other vehicle occupants.  One exception was a stroller-type wheelchair with triangulated frame and seat-to-backrest bracing that maintained a midsize male crash dummy in a seated position with head support during the rear impact test.

The literature review covered all areas related to rear-impact injuries, including: 1) injury patterns, injury mechanisms, and injury criteria, 2) appropriate impact severities for rear-impact testing, 3) different anthropomorphic test devices (ATDs) for use in rear-impact testing, 4) federal and international safety standards related to rear-impact protection, and 5) restraint design for rear-impact protection.  Additional analyses of the NASS (National Automotive Sampling System) database were conducted to determine the distribution of rear-impact crash severities and the results were used to further establish the most appropriate rear-impact crash pulse for use in future dynamic testing and standards development related to transportation of wheelchair-seated occupants.  In particular, the NASS analysis compared the distribution of rear-impact crash severities for all passenger cars to the distribution of crash severities to passenger vehicles most frequently used for private vehicle transportation of wheelchair-seated passengers, such as minivans and vans.

Sled impact testing of a load-cell instrumented seatback mounted on the surrogate wheelchair base was used to quantify seatback strength requirements in relation to seatback deflection properties under rear impact loading situations.  In addition, the relationship between ATD-imposed loads on the seatback and rearward ATD head excursions were evaluated with the goal of determining optimum backrest performance for both occupant retention and injury reduction.  Results of sled-impact testing were supplemented by computer simulations of wheelchairs and occupants in rear impact loading which were used to investigate seatback moments at the three seatback stiffness levels.

A compilation of wheelchair frame and seatback geometry dimensions was conducted to help formulate design guidelines for vehicle-mounted head and back supports.   These data, along with the test results and computer simulations will be used to help WTORS manufacturers develop and test prototype vehicle-anchored backrest and headrest components that offer improved occupant protection under for forward-facing wheelchair occupants in rear impacts. 

The results of research and testing in Task 2a have been used to propose design specifications and performance criteria for wheelchairs and WTORS that provide improved protection to forward-facing wheelchair users in rear impacts.  These specifications and criteria, and the associated test methods, for rear-impact protection will be used to augment the frontal-impact requirements of wheelchair and WTORS standards.

Last updated: August 30, 2006

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