Traveler protection during transit and vehicle impact is the primary objective of occupant restraint design, including occupant restraints of wheelchair-using travelers in transit vehicles. The objective of this project was to develop and evaluate new occupant restraint design concepts with focus on minimizing the efforts to operate the system while maintaining the crash protection of the wheelchair-using traveler.
The investigation started with the formation of the design criteria based on multiple inputs from a resource panel of experts, wheelchair users, transit administrators, vehicle operators, human factors testing of wheelchair-using travelers, and an experienced public transit vehicle designer.
A survey was developed and disseminated to administrators at 12 transit authorities throughout the country and vehicle operators involved with transportation of wheelchair users. Overall, the survey indicated conflicting information on priorities of safety, lack of use of lap and shoulder belts, fastening time between fixed route and paratransit application, and the need for alternatives to the existing occupant restraint designs. New design criteria were indicated for restraints to be used independently and rapidly by many wheelchair users with reduction of stop dwell time and driver involvement.
The human factors testing established anthropometric envelopes of a wheelchair occupant’s seated posture, reach, hand strength, and functional ability to position the wheelchair.
The design criteria from all these inputs were finalized and tabulated. The criteria established specifications for activation time, user independence, durability, component locations, operating hand function requirement, body size accommodations, and crash safety in terms of load and deflection parameters.
Using the design criteria, three conceptual models of wheelchair occupant restraint systems were developed and investigated. The early concepts of stanchion-mount and wall-mount designs were evaluated but not implemented because of obtrusive bulkiness for the first and incompatibility with vehicle structural design for the second. In previous sled impact testing (30 mph, 20-g and 5-g lateral impact) the stanchion-mount design performed well and appeared to be superior to the 3-point belt restraints.
The final panel-mount design was developed and refined, and a full-scale prototype was built for limited user tests and strength evaluation. The concept is illustrated in Figure 1. To minimize costs and to enhance commercial appeal, an effort was made for a simple design with off-the-shelf components and cost-effective tolerances.