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WHEELCHAIR TIEDOWN AND OCCUPANT RESTRAINT SYSTEMS FOR USE MOTOR VEHICLES
Foreword—For people with disabilities who are unable to transfer from their wheelchairs when traveling in motor vehicles, the wheelchair must serve as the vehicle seat. This usually means that the occupant restraint system installed by the vehicle manufacturer cannot be used to provide protection in a crash. In addition, the wheelchair must be secured to the vehicle so that it does not impose forces on its occupant and/or become a hazard to other vehicle occupants in a collision or sudden vehicle maneuver. Providing occupant protection for the wheelchair-seated occupant, therefore, requires that aftermarket equipment be installed to secure the wheelchair and restrain the wheelchair user.
This Recommended Practice applies to the design and performance of motor-vehicle adaptive equipment referred to as wheelchair tiedown and occupant restraint system or WTODS. It is the purpose of this document to encourage the design, testing, installation, and use of WTODS equipment that will provide effective wheelchair securement and occupant restraint in a frontal collision, and that will be comparable in crash performance to seat securement and occupant restraint systems provided by the vehicle manufacturer. While the primary concern is to reduce the potential for injury to wheelchair-seated occupants involved in a frontal vehicle crash, it is anticipated that achievement of improved occupant protection will also result in increased driver and passenger safety and comfort during normal travel. The provisions of this document should not be used to discourage people with disabilities using motor vehicle transportation or to limit access to, and availability of, motor vehicle transportation to wheelchair users.
Since manufacturers of WTORS are generally not able to control or specify the end use of their products, the 48-km/h, 20-g sled impact test specified in Appendix A is intended to qualify WTORS for use in vehicles with a gross vehicle weight of less than 7000kg. In larger vehicles, it may be possible to provide safe transportation using WTORS that do not comply with the level of crash severity used in this document.
As with any vehicle seat, the wheelchair is an important component of the occupant protection system, and also contributes to the stability and comfort of the wheelchair-seated occupant during normal travel. Design and performance of wheelchairs used as seats in motor vehicles is addressed in a separate, but related, ANSI/RESNA Standard now under development.
Design Requirements
1. Complete WTORS--WTORS shall:
a. Be for use with only one wheelchair and one occupant at a time .
b. Not require components of wheelchair tiedowns and occupant restraints to pass through the
wheels of a wheelchair .
c. Provide for release of both the wheelchair and the occupant within 60s by a single attendant or
wheelchair user without the use of tools .
d. Not require removal of wheelchair frame material, drilling into the wheelchair frame,
deformation of the wheelchair, welding, or the use of an adhesive process, during installation,
unless the WTORS is intended for a srecific wheelchair and the modifications are approved by
the wheelchair manufacturer .
e. Once installed, be operable without tools .
f. Include only hardware and fittings that are permanently connected to the WTORS or a
WTORS subassembly .
g. Be designed to prevent unintentional loosening of all threaded fasteners .
h. Include a manual override in case of power failure for any power-operated mechanisms of
tiedowns or restraints .
i. Include anchorage fasteners and hardware, and/or specifications for such hardware, that are
based on the material, size, and quantity of anchorage fasteners used in the simulated frontal
inpact test of Appendix A .
2. Wheelchair Tiedowns--Wheelchair tiedowns and tiedown components shall:
a. Not depend on the wheelchair brakes .
b. Be designed so that securement of the wheelchair is accomplished by the tiedown only and not
by the occupant restraints .
c. Provide a means to eliminate free movement of the wheelchair without the use of tools .
d. If the WTORS includes a four-point strap -type tiedown, each strap assembly shall provide for
manual adjustment in length without the use of tools, such that the adjustment ranges of front
and rear straps enable achieving the minimum and maximum lengths indicated in Table 1, with
at least 25 mm of webbing extending from the adjustment mechanisms.
TABLE 1--MIMIMUM ADJUSTMENT RANGES FOR FOUR-POINT TIEDOWN STRAPS：
Strap Assembly Location Mimimum Length mm (in) Maximum Length mm (in)
Rear 485(19) 740(29)
Front 410(16) 710(28)
e. Have securement-point end fittings of four-point tiedowns that are compatible with the
securement-point structural member of the surrogate wheelchair illustrated in Figure E4 .
f. Include a device to indicate, by visual or auditory means, when a docking-type tiedown is
properly engaged .
3. Occupant Restraints--WTORS shall either be designed to use the vehicle OEM passenger or
driver restraint, or shall include an occupant restraint that complies with the following
requirements:
3.1.The occupant restraint portion of the WTORS shall include both pelvic and upper torso restraints .
3.2 Occupant restraints may be designed to anchor directly to the vehicle, to components of the wheelchair tiedown, or to tiedown components fastened to the wheelchair. Occupant restraints shall not be designed with anchorages that rely on the transmission of restraint loads through the wheelchair structure unless the WTORS is designed for a specific wheelchair and the WTORS meets the requirements of 6.2 when the combination of wheelchair and WTORS is tested according to Appendix A .
3.3 The lengths of pelvic and upper torso restraints shall be manually adjustable without the use of tools .
3.4 When the WTORS is set up and measured as specified in Appendix B, pelvic restraints and, if applicable, their anchor points or guide points, shall:
a. Achieve side-view projected angles that fall within the zone shown in Figure 4b .
b. Achieve projected rear-view angles and locations within the zones shown in Figure 4a .
c. Provide sufficient length adjustment to allow the pelvic restraint, measured from anchor point to anchor point, to be both increased and decreased by 200 mm with at least 25 mm of webbing extending through the restraint end fittings at all times .
3.5 When the WTORS is set up and measured as specified in Appendix B, upper torso restraints shall provide for sufficient length adjustment to extend an additional 200 mm, and shorten by 300 mm, with at least 25 mm of webbing extending through the restraint end fittings at all times .
4（a） 4(b)
FIGURE 4
NOTE—Note that angles indicated are obtained by projecting the angle of the pelvic restraint onto a vertical plane to the wheelchair reference plane (side view), or onto a vertical plane that is perpendicular to the wheelchair reference plane (rear view) .
3.6 For WTORS that include upper-anchor points or upper-guide support structures for shoulder or harness restraints, the locations of these anchor points or supporting structures shall:
a. Be sufficiently adjustable in height to be located at or above the shoulder levels of the intended user .
b. Be located at least 1100 mm above the wheelchair ground plane so as to be near or above the shoulder height of wheelchair seated occupants .
NOTE1—The anchor point may be located below 1100 mm if an upper-guide support is located at or above 1100 mm .
NOTE2—Although FMVSS 210 allows for the upper torso restraint anchor points to be located a significant distance below the occupant’s shoulder level, such locations are considered to be undersirable and not in compliance with this document since they could result in downward loading on the occupant that can produce spinal injuries .
3.7 The junction of the shoulder and pelvic restraints of three-point restraints shall be located not less than 150 mm from the ATD centerline when installed as specified in Appendix B .
3.8 An airbag shall be used only as a supplementary occupant restraint in conjunction with a wheelchair tiedown and belt-type occupant restraint that comply with the requirements of this document .
3.9 Performance of the WTORS shall not depend on an airbag to comply with this document .
4. Test Report—The WTORS manufacturer shall have documentation on file and available that includes:
4.1 Statements concerning compliance of the WTORS with the Design Requirements of 4.2 through 4.3 including:
a. Minimum and maximum tiedown strap lengths of four-point strap tiedowns in comparison to the requirements of Table 1 .
b. Whether the end-fitting geometry of four-point tiedowns is compatible with the end-fitting geometry of Figure E4 .
c. The angle of pelvic restraints when setup according to Appendix B .
d. The range of length adjustment in the pelvic restraint when set up and measured as specified in Appendix B .
e. The range of length adjustment in the upper-torso restraints when set up and measured as specified in Appendix B .
f. The height or height-adjustment range of upper-torso restraint upper-anchor upper-guide support provided with the WTORS, and a statement of whether the height complies with 4.3.6 .
g. The distance of the pelvic/shoulder restraint interface of three-point restraints from the ATD centerline when set up and measured according to Appendix B .
4.2 Statements concerning compliance with the requirements of :
a. FMVSS 209 as specified in Table 2 .
b. FMVSS 302 concerning flammability of WTORS webbing material .
4.3 Statements concerning compliance with the Frontal Impact Test of Appendix A, including :
a. A description of the test facility, including the type of impact simulated, instrumentation and signal processing techniques, the frame speed for each film and/or video produced, methods for measuring sled velocity change and deceleration, methods used to measure ATD and test wheelchair excursions, and the accuracy of excursion measurements .
b. A statement of whether the sled deceleration pulse complied with A.4.3 and Figure A1, including the duration of the pulse, and the number of cumulative milliseconds that the deceleration exceeded 15 g and 20 g .
c. The measured or calculated value of the test delta V .
d. A full identification of the WTORS, anchorage fasteners, test wheelchair, and ATD used .
e. Pretest measurements documenting the locations of all WTORS anchorages relative to point P of the test wheelchair .
f. The side-view, front-view, and rear-view projected angles of all tiedown straps and pelvic restraints relative to the horizontal or vertical, as appropriate .
g. A description of the test setup including a statement about any parts or fasteners used ih the test that were not provided by the WTORS manufacturer .
h. Whether the ATD remained in the test wheelchair .
i. Whether the test wheelchair remained on the test platform .
j. The change in the orientation of the test wheelchair reference plane, if measurable, in comparison with the initial test orientation .
k. Identification of any WTORS load-carrying parts that showed visible signs of tearing, fragmentation, fracture, or complete failure, that were not designed to rear or fail in the manner noted .
l. The peak horizontal excursions specified in 6.2.d, and whether any of the excursions exceeded the limits in Table 3 of this document .
m. A statement as to whether the ATD and test wheelchair could be released from the WTORS without the use of tools .
n. A statement as to whether the ATD was loaded by the test wheelchair based on the results of the calculation in 6.2.e .
4.4 Statements concerning compliance of appropriate WTORS components with the Test for Partial Engagement of Appendix C, including :
a. Full identification of the WTORS system and the securement and anchorage components tested .
b. A description, including photographs if necessary, of the manner of each partial engagement tested .
c. A description of the procedure used to apply the separating force .
d. The results of each test, i.e., the securement or anchorage mechanism either separated or remained engaged .
4.5 Statements concerning compliance of any strap assemblies of wheelchair tiedowns with the Test for Webbing Slippage at Adjustment Devices of Appendix D, including :
a. Full identification of the WTORS system, type of webbing, and each adjustment device tested .
b. A description of the test apparatus and procedure .
c. The amount of webbing slippage at each adjustment device tested .
d. A statement as to whether the 25 mm limit was exceeded for each adjustment device tested .
e. A statement as to whether all adjustment devices of the wheelchair tiedown portion the WTORS passed the test .
5. Definitions—For the purposes of this document, the following definitions apply:
5.1 Anchorage—An assembly of hardware and fittings by which loads are transferred directly from the wheelchair tiedown to the vehicle or from the occupant restraint to the vehicle, wheelchair, wheelchair tiedown, or vehicle seat base .
5.2 Anchor Point—A point (area) on a vehicle, wheelchair, wheelchair tiedown, or vehicle seat base to which an anchorage is attached .
5.3 ANSI—Abbreviation for American National Standards Institute .
5.4 Anthropomorphic Test Device (ATD) –An articulated analog of the human body used to simulate a motor-vehicle occupant in a crash environment .
5.5 Automatic-Locking Retractor—A retractor incorporating adjustment by means of a positive self-locking mechanism which is capable, when locked, of withstanding restraint forces (from SAE J1834) .
5.6 Back Restraint—A device or system intended to limit rearward movement of the occupant by providing support to the back of the torso .
5.7 Belt—A length of energy-absorbing webbing material used as part of an occupant restraint .
5.8 Docking-Type Tiedown—A wheelchair securement device whose engagement is initiated as a result of the wheelchair rolling into the proper position .
5.9 Emergency-Locking Retractor—A retractor incorporating adjustment hardware by means of a locking mechanism that is activated by vehicle acceleration, webbing movement relative to the vehicle, or automatic action during an emergency, and that is capable, when locked, of withstanding restraint forces (from SAE J1834) .
5.10 End Fitting—Anchorage and securement hardware to which tiedown and occupant restraint webbing is fastened and which attaches directly to the anchor points and securement points on the wheelchair, tiedown system, or vehicle .
5.11 Fasteners—Devices used to secure, by mechanical means, other components or parts in place .
Note—These include, but are not limited to:bolts, nuts, screws, pins, rivets, and clamps .
5.12 Forward Facing—Orientation in which the wheelchair-seated occupant faces the front of the vehicle with the wheelchair reference plane within 10 degrees of the longitudinal axis of the vehicle .
5.13 Four-Point Tiedown—A wheelchair tiedown system that attaches to the wheelchair frame at four separate points and anchors to the vehicle at four separate anchor points .
Note—The typical four-point tiedown system uses four tiedown straps, with two attached to the front portion of the wheelchair and two attached to the rear portion .
5.14 Harness—An occupant restraint consisting of at least one belt designed to provide pelvic restraint and two shoulder or torso belts that apply forces to both shoulders .
5.15 Head Restraint—A device intended to limit rearward displacement of the occupant’s head .
5.16 Impact Simulator—A device for accelerating, decelerating, or a combination of decelerating and accelerating, a section of a vehicle or simulated vehicle structures, including instrumentation for measuring pertinent data (from SAE J850) .
5.17 Impact Sled—That part of an impact simulator on which components can be mounted for impact testing .
5.18 Independent Occupant Restraint—An occupant restraint that anchors directly to the vehicle or vehicle anchored components that are separate from the wheelchair and wheelchair tiedown .
Note—This is also known as a parallel restraint system .
5.19 Integrated Occupant Restraint—An occupant restraint for which the anchor points for the pelvic-restraint, or both pelvic and shoulder- restraints, are located on the wheelchair, or on tiedown components not fastened to the vehicle .
5.20 Occupant Restraint Anchorage—An assembly of hardware and fittings by which loads are transferred directly from the occupant restraint to the vehicle, wheelchair, wheelchair tiedown, or vehicle seat dase .
5.21 Occupant Restraint—A system or device for restraining the occupant in a vehicle to prevent or minimize contact with the vehicle interior components, and to prevent ejection during a crash (from SAE J2094) .
5.22 OEM—Abbreviation for Original Equipment Manufacturer .
5.23 Pelvic Restraint—That portion of a seat-belt assembly intended to limit movement of the pelvis .
Note—Other terms with similar meaning are lap belt, lap restraint, and lower torso restraint .
5.24 Point P—A reference point that lies at the cross-sectional center of a 100 mm diameter disc positioned with the longitudinal axis perpendicular to the wheelchair reference plane, such that the curved surface of the disc contacts with the backrest and the upper surface of the seat .
5.25 Postural Support—A component used to support a person in a desired position, but that is not usually intended to provide occupant restraint in a vehicle impact .
5.26 Securement Hardware—End fittings of a wheelchair tiedown system that connect to the wheelchair .
5.27 Securement Point—Location on the wheelchair frame to which a wheelchair tiedown end fitting connects .
5.28 Strap—A length of webbing material used as a part of a wheelchair tiedown .
5.29 Surrogate Wheelchair—A rigid, reusable device used to simulate a wheelchair for the purpose of testing a WTORS .
5.30 SWC—Abbreviation for surrogate wheelchair .
5.31 Test Wheelchair—A production, prototype, or surrogate wheelchair used to conduct tests specified in this document .
5.32 Wheelchair Tiedown Anchorage—An assembly of hardware and fittings by which loads are transferred directly from the wheelchair tiedown to the vehicle .
5.33 WTORS—Abbreviation for wheelchair tiedown and occupant restraint system .