SP-2: Side and Rear Impact

Importance of the problem

Description of the need and target population

In the real world, occupants of motor vehicles are injured and killed in different types of motor vehicle crashes with widely varying directions of impact to the vehicle in which they are riding. Although no two crashes are exactly the same, and many motor vehicle accidents involve more than one type of impact event, the types of motor crashes are generally classified into the four different categories of frontals, side, rear, and rollovers. There are also different sub categories for each of these types, such as offset frontals, barrier-type frontals, frontals with under ride or override, and pole-type frontals.

Associated with each type or category of crash are different probabilities of the crash event, different distributions of crash severities, and different patterns, causes, and risks of injuries for a given type of vehicle and/or mode of transportation. In a complete occupant protection system, one must design the vehicle, the seat, and the restraint systems to deal with the full spectrum of crash types and associated causes of injury.

In the United States, side and rear impacts are the second and third most common type of vehicle impact, respectively after frontal impacts, that result in injuries to occupants (Traffic Safety Facts 1998). Side impacts account for approximately 27 percent of motor vehicle crash fatalities and 30 percent of motor vehicle crash injuries. Rear impacts account for approximately five percent of motor vehicle crash fatalities, a quarter of motor vehicle crash injuries, and are associated with serious medical consequences and significant societal costs.

Because frontal crashes constitute more than 50% of serious and fatal injury-producing passenger motor-vehicle accidents, these types of crashes have been given the highest priority in establishing federal motor vehicle safety standards (FMVSS). Following this example, research, testing, and standard development conducted to date for wheelchair-seated travelers have been focused exclusively on providing improved crash protection in frontal impacts. Thus, both U.S. and ISO standards for wheelchair tiedown and occupant restraint systems or WTORS (SAE J2249 Wheelchair Tiedowns and Occupant Restraints for Use in Motor Vehicles and FMVSS 222 School Bus Passenger Seating and Crash Protection ) and for transit wheelchairs (Section 19 ANSI/RESNA Vol. 1 Wheelchairs Used as Seats in Motor Vehicles) require that equipment be tested statically or dynamically for conditions that are representative of loading generated in a frontal crash. In developing these initial standards, and in doing the research and testing necessary to establish test procedures and performance criteria, the need to address the concerns of wheelchair occupant safety for other modes of impact was clearly recognized, but was placed on hold until the primary concern of frontal crash protection had been adequately deal with.

It is now time to address more directly the safety concerns of wheelchair-seated occupants with regard to their potential involvement in rear and side impacts. The wheelchair transportation safety RERC provides an excellent opportunity to investigate these side-impact and rear impact safety issues and needs of wheelchair-seated occupants, and to develop test methods, design and performance requirements, for inclusion in additional voluntary standards. In this priority, the research needed to develop these methods, requirements, and standards for side- and rear-impact protection will be conducted. In the process, commercially available products that comply with SAE J2249 and WC/19 will be evaluated with regard to their performance under these impact conditions, and prototypes of improved products and product components will be developed.

Beneficial impact on target population, including service providers

The two tasks of this priority will ultimately result in a reduction of injury risk to wheelchair seated travelers involved in rear and side impacts. The first step toward this result will be the development of design and performance criteria, and associated test methods, for improved safety performance of wheelchairs, wheelchair components, and WTORS in rear and side impacts. These criteria and test methods will be implemented in new ANSI/RESNA and ISO safety standards that will encourage the development of improved products by manufacturers. As has been the case for frontal impact protection, these standards will provide manufacturers clear targets for further improving the design and performance of commercially WTORS and transit wheelchairs with regard to rear and side impacts. The information from the research phases of this priority will be valuable to service providers who must make decisions about the methods and equipment used to secure wheelchairs and restraint wheelchair occupants in different types of vehicles.

Responsiveness to priority

This priority is in direct response to announced priority (b): “Investigate and report on safety issues, including both kinematics and biomechanics, related to wheelchair-seated occupants subjected to side and rear impact crashes.”

The priority involves two primary Tasks. The first addresses the issues and concerns of providing wheelchair occupant protection in rear impacts. The second addresses issues and concerns related to wheelchair occupant injury risk in side impacts. Although the announced priority calls only for researching and reporting on the issues of rear and side-impact protection, this is not considered to be a sufficient treatment of this priority. Therefore, in addition to investigating the safety issue and biomechanics of injury in rear and side impacts, each Task of this priority will also involve development efforts related to establishing appropriate design and performance criteria, as well as the development of prototype devices and systems that comply with those criteria in collaboration with manufacturers through the technology transfer portion of the RERC.

Overall objectives

The overall objective of this priority is to reduce injury risk to wheelchair-seated occupants who are involved in side and rear crashes. This will be accomplished by:

1. researching and summarizing the state of knowledge regarding crash statistics and distributions of crash severities of side and rear impacts for different types of motor vehicles,
2. researching and summarizing the state of knowledge of occupant kinematics, mechanisms of injury, and injury patterns in side and rear impacts,
3. synthesizing results of (1) and (2) into proposed design and performance criteria, and associated test methods for evaluating wheelchair securement systems, wheelchairs, wheelchair components, and occupant restraint systems with regard to reducing injury risk to wheelchair-seated occupants involved in side and rear impacts,
4. conducting static and dynamic tests using existing WTORS and wheelchair/seat systems, as appropriate, to confirm and refine proposed test methods and performance requirements and criteria,
5. developing crash-victim simulation (CVS) models for simulating wheelchair and wheelchair occupant response to rear and side impacts,
6. using the developed CVS models and dynamic testing to assess the loads on wheelchairs and WTORS in side and rear impacts,
7. using the developed CVS models and dynamic testing to assess the injury risk to wheelchair seated occupants in rear and side impacts, and
8. in collaboration with wheelchair and WTORS manufacturers, developing prototype wheelchair and WTORS systems and components to achieve improved performance with regard to established criteria in side and rear impacts.

Organization of work plan

Dr. Lawrence Schneider will supervise the research and development activities on the two research and development tasks of this priority. Ms. Miriam Manary and Dr. Gina Bertocci will serve as co-investigators, and will carry out the various research, testing, and modeling efforts, with assistance from graduate students.

The two tasks of this priority will be conducted in sequence over the full duration of the five-year program. In the first 2-1/2 years, the effort will focus on the concern for rear-impact protection, and in the final 2-1/2 years, the efforts will be directed to side-impact protection.

Last updated: April 11, 2002