What is the difference between an integrated and an independent occupant restraint system?
An independent occupant restraint system is a vehicle-anchored belt restraint system that is anchored “independent” of the occupant’s seat or wheelchair to the vehicle structures. With an integrated restraint system, the anchor points for the restraint system are on the seat or wheelchair – i.e., it is a seat- or wheelchair-anchored seatbelt system. Integrated restraint systems are becoming more common in automobiles because the belts generally fit and perform better when they are anchored closer to the occupant on the vehicle seat. It is also possible to have a partially integrated restraint system, where only the pelvic belt is anchored to the wheelchair or vehicle seat, but the upper end of the shoulder belt is anchored to the side-wall of the vehicle. This is what is required as an option on all WC19 wheelchairs. If a wheelchair user chooses this option, they can have a pelvic/lap belt installed on the wheelchair that will include hardware for a standard interface connection to the lower end of a vehicle-anchored shoulder belt.
It is also possible to have a totally integrated belt restraint system where the anchor points for both the upper and lower torso belts are on the wheelchair. However, the upper anchor points will place high forces on the upper part of a wheelchair backrest in a frontal crash, and most wheelchair backrests would not be able to withstand these forces without significant design modifications. The totally integrated restraint system is most feasible and most important for smaller children, but the partially integrated pelvic/lap belt should be feasible for most wheelchair users and will improve pelvic belt performance, reduce the tendency for lap-belt “submarining” (i.e., the occupant’s hips sliding under the lap belt during a crash), and reduce invasion of the wheelchair user’s personal space when installing a belt restraint in a motor vehicle. For these reasons, WC19 requires wheelchairs to provide the wheelchair user with the option of using a wheelchair-anchored pelvic belt.
Beginning in December 2015 (three years after initial publication of WC18), WTORS for general use are required to perform an additional crash test where the ATD is restrained by a surrogate pelvic (lap) belt anchored to the test wheelchair, thereby increasing the frontal-impact loads on the rear tiedown straps of four-point, strap-type tiedown systems, or on other types of securement devices.
Note: The term restraint is used exclusively in reference to the wheelchair occupant and the term tiedown or securement is used exclusively in reference to the wheelchair. A wheelchair is not restrained but is tied down or secured. An occupant is not secured, but is restrained in a motor vehicle.