BACKGROUND

In a recent University of Pittsburgh survey of 596 wheelchair users in 45 states, it was found that 26% of the respondents remained seated in their wheelchairs while driving personal vehicles and that these wheelchair-seated drivers had a significantly higher frequency of crash involvement than individuals who transfer to the vehicle seat (1).  Also, a study of vehicle crashes involving one or more wheelchair-seated occupants by the University of Michigan Transportation Research Institute (UMTRI) reported that, of 22 wheelchair-seated occupants involved in crashes, 7 individuals (nearly one third) died from crash-related injuries.  The majority of these crashes were minor to moderate in severity and would not have resulted in fatal injuries to occupants using the vehicle seats and restraint systems (2).  

As part of an effort to improve transportation safety and crash protection for wheelchair–seated travelers, Section 19 of ANSI/RESNA Wheelchair Standards/Volume 1, also known as WC19, was developed to establish design and frontal-impact performance requirements for wheelchairs intended for the use as seats by passengers in motor vehicles (3).  In addition to requiring the wheelchair to demonstrate crashworthiness in a 48-kph frontal sled impact test when secured by a four-point, strap-type tiedown system, this standard requires evaluation of wheelchairs with regard to accommodation of vehicle-anchored lap/shoulder belt restraints (Annex E of WC19). This is because the effectiveness of belt restraints in protecting occupants in frontal crashes depends on good contact of both lap and shoulder belts with skeletal regions of the occupant prior to the collision, so that the belts will provide restraint as soon as possible after onset of the impact. A properly placed lap belt is positioned low on the pelvis near the thigh-abdominal junction and a properly positioned shoulder belt will travel over the middle of the outboard shoulder and across the center of the chest. If belt restraints are not initially in contact with the body, the likelihood of serious injuries from belt loading and occupant contact with vehicle interior components is increased.

Using the procedures of WC19 Annex E, the wheelchair is rated on factors related to the ease of using and positioning lap/shoulder belt restraints in an optimal location relative to the occupant and wheelchair components.  However, the belt-accommodation rating procedure in WC19 is currently limited to evaluating seatbelt placement by an attendant, and is therefore not particularly applicable to wheelchair-seated drivers, and particularly drivers who require a completely passive belt restraint system (requiring no action by the occupant). 

OBJECTIVE

The objective of this study was to identify factors, and particularly wheelchair design issues, that facilitate or interfere with proper use and fit of belt restraints for people who drive a personal vehicle while seated in their wheelchair. Although data were also collected for 8 wheelchair-seated front-row passengers in private vehicles, this paper is focused on the results for the wheelchair-seated drivers who require independence for wheelchair securement and use of vehicle belt restraint systems.

METHODS

Eighteen individuals who drive their own vehicle (typically a full-size van or minivan) while seated in a wheelchair were recruited for the study from the southeastern Michigan (n=10) and the western Pennsylvania areas (n=8), and were tested at UMTRI and the University of Pittsburgh, respectively ¹ . Subjects were videotaped and photographed while moving into the driver station and preparing for travel. Measurements were then taken to document the position of the lap and shoulder belts relative to wheelchair components and the wheelchair user’s body. The type of wheelchair armrest was noted and categorized as a “closed-front” armrest if any structural component connected the front or middle portion of the armrest to the wheelchair frame below, as shown in Figure 1a.  An armrest was categorized as “open-front” if there were no components connecting the armrest to the wheelchair frame except near the seatback, i.e., the armrest was cantilevered and anchored to the wheelchair only at the seatback as shown in the example in Figure 1b. 

For each subject, two ratings were assigned by the investigator.  One rating was based on the ease with which the wheelchair-seated driver positioned the belt restraint in their usual manner, regardless of how properly the belt was positioned.  In accordance with Table 1 of Annex E, the investigator assigned a rating of “good” if the occupant belts were positioned without inserting the belt webbing into a narrow opening of less than 25 mm between wheelchair components.   A rating of “acceptable” was assigned if the subject inserted the belt webbing into a narrow space of less than 25 mm between wheelchair components.  A “poor” rating was assigned if the subject threaded the belt latch plate, buckle or belt webbing through an opening created by wheelchair components. The second rating was assigned based on the location of pelvic belt contact using the criteria in Table 4 of WC19 Annex E.  A rating of “good” was assigned if the pelvic belt made contact low on the subject’s pelvis at or near the thigh-abdominal junctions.   A rating of “acceptable” was assigned if the pelvic belt made contact with the upper part of the subject’s pelvis due to interference by wheelchair components.  A “poor” rating was assigned if the pelvic belt contacted the subject above the pelvis and on the abdomen because of interference by wheelchair components.

RESULTS

Of the 18 wheelchair-seated drivers tested, three used manual wheelchairs with power assist and 15 used powered wheelchairs. One manual wheelchair did not have armrests, 4 wheelchairs (2 manual and 2 powered) had armrests that were characterized as open-front, and 13 wheelchairs (all powered) had armrests that were closed-front.  Of the thirteen wheelchairs with a closed-front armrest, 12 had a desk (or L-shaped) armrest and one had armrests that connected to the wheelchair in the front and back by arc-shaped components.  Of the 18 subjects, 13 used the original equipment manufacturer (OEM) lap/shoulder belt systems with an after-market inboard buckle receptacle attached to a cable stalk or a length of webbing anchored to the vehicle floor.  Two subjects used an after-market lap/shoulder belt system, and one used a wheelchair-anchored lap belt that was routed between the wheelchair armrests and seatback and a passive vehicle-anchored shoulder belt.  Two other wheelchair-seated drivers did not use any pelvic-belt restraint, but relied on a shoulder belt only.

Pelvic Belt Routing With Closed-Front Armrests

As previously noted, subjects were rated on the ease-of-belt-restraint-use in the manner that they typically positioned the belt restraint.  Five subjects routed the pelvic belt around the front of the forward-most vertical structural member of the closed-front armrests on both sides of the wheelchair, while two subjects routed the belt around the front of the armrest on the outboard side of the wheelchair and over top of the wheelchair armrest on the inboard side.  Two subjects routed the pelvic belt over the top of both wheelchair armrests and one subject routed the belt around the front of the armrest on the outboard side of the wheelchair and around the seatback post on the inboard side of the wheelchair, which is considered a gross misuse of the belt restraint. Routing of any portion of the pelvic belt over the top of the armrests usually resulted in the pelvic belt being positioned high on the driver’s abdomen and not in contact with the pelvis.

Ratings for Ease of Positioning the Belt Restraints

The ratings for ease of belt positioning for one subject was not included in this analysis because the belt-restraint was grossly misused, as previously described. Figure 2 compares these ratings for the two different wheelchair armrest configurations. All 5 subjects with open-front armrests received a “good” rating for ease-of-use.  Of the 12 subjects with closed-front armrests, 11 received a “good” rating for ease-of-use, and 1 received an “acceptable” rating due to placement of the belt webbing into narrow spaces between components of the armrests. A Chi-Squared test showed that the ratings for “ease-of-use” are not statistically different for the two categories of wheelchair armrests (p=0.51).

Ratings for Pelvic-Belt Contact Location

The contact location of the pelvic belt on the wheelchair driver was evaluated for 10 subjects with closed-front armrests and 5 subjects with open-front armrests.  The ratings were not included for one subject who grossly misused the belt restraints and for the 2 subjects who only used a shoulder belt.  Figure 3 compares the ratings for pelvic-belt contact location for the two wheelchair armrest configurations. For all 5 wheelchairs with open-front armrests a rating of “good” was assigned.  For the 10 wheelchairs with closed-front armrests, pelvic-belt contact was rated “good” in 4 cases, “acceptable” in 2 cases, and “poor” in 4 cases.  However, a Chi-Squared test reveals that these differences do not reach statistical significance (p = 0.082).

DISCUSSION AND CONCLUSIONS

When interpreting the results of this study, it’s important to appreciate that that the ratings for ease-of-belt-restraint-use were assigned by the investigator based on observation of the wheelchair user’s positioning the belt restraints in their usual manner, and not on the ease for achieving optimal or proper belt fit.  All subjects except one with a wheelchair having a closed-front armrest achieved a rating of “good” for ease-of-use, indicating that drivers will tend to do what is easiest in using the belt restraint, regardless of whether this results in proper belt fit.  Although the differences for ratings of pelvic-belt location for closed-front and open-front armrests were not found to be statistically significant, this is most likely due to the small sample size of subjects.  In fact, when the results for the 8 wheelchair-seated right-front passengers are included in the analysis, the differences do reach statistical significance (p=0.019), with the open-front armrest resulting in “good” pelvic-belt location much more frequently than closed-front armrests. The results of this study therefore suggest that use of an open-front armrest greatly facilitates proper pelvic belt fit for wheelchair-seated drivers and that a closed-front armrest often interferes with proper belt fit, even when the armrest is of the L-shaped desk-type configuration. 

Because the effectiveness of belt restraints in protecting drivers in frontal crashes depends on proper belt positioning on the occupant prior to the collision, which is largely dependent on the ease of achieving proper belt fit, it can be expected that the use of open-front armrests on the wheelchair will markedly increase occupant crash protection for wheelchair-seated drivers.  It can also be expected that open-front wheelchair armrests will facilitate proper restraint positioning by vehicle operators and caregivers who assist wheelchair-seated passengers when traveling in private, para-transit, and public transportation vehicles.  The results of this study provide information for wheelchair manufacturers that seek to improve wheelchair and armrest designs to better accommodate proper seatbelt use and positioning, and therefore the overall transportation safety for wheelchair-seated drivers.  The results will also be useful for wheelchair prescribers when recommending wheelchairs and armrest configurations for people who expect to drive a personal vehicle while seated in their wheelchair.

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