These research summaries have been created to help those who prefer reading current research in a less formal style of writing. Anyone who wants to read the original research article (as it was published in the journal or conference proceedings) can use the reference to locate the research in that form.
One of the main emphases of the past research at the (University of Pittsburgh’s) Rehabilitation Engineering Research Center for Wheelchair Transportation Safety was the design and development of wheelchair integrated restraint systems, (WIRSs). These systems are intended for wheelchair users who sit in their wheelchairs while in moving vehicles. WIRSs are much like seatbelts in conventional cars. They restrain both the hips and shoulders and are built directly into the wheelchair.
WIRSs have several advantages over conventional wheelchair occupant restraint systems, systems that are built into the floor and walls of the vehicle instead of directly into the rider’s wheelchair. First, WIRSs can be custom-fitted, so they fit better and more comfortably than vehicle-mounted restraint systems. The better the fit of a restraint system, the better that system is at preventing injury in the event of a crash. Secondly, WIRS are usually easier to fasten than vehicle-mounted restraint systems, allowing some wheelchair users to secure their belts independently. Finally, because WIRSs fit better and are easier and faster to use, many more people are likely to take the time to buckle up. Click here to read the results of a study that examined the reasons why vehicle-mounted wheelchair occupant restraint systems were not worn by users. (Preliminary evaluation of wheelchair occupant restraint systems).
The results of a previous study conducted at The University of Pittsburgh indicate that WIRSs meet the automotive industry’s standards for injury prevention, but much more research needs to be conducted before WIRSs can be made commercially available.
As a result of this research, the WC19 safety standard now requires that wheelchairs provide the wheelchair user with the option of using a dynamically tested wheelchair-anchored pelvic belt to which a vehicle-anchored shoulder belt can be readily connected.
This summary is based on the following original article: Bertocci, G., DongRan H., Deemer, E., & Karg, P. (2001). Evaluation of wheelchair seating system crashworthiness: "Drop hook" type seat attachment hardware. Archive of Physical Medicine and Rehabilitation, 82, 534-40.
Injury Risk Assessment and Prevention Laboratory, Department of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA
Many wheelchair users sit directly in their wheelchairs when riding in motor vehicles. Often, this is because they have little or no ability to transfer out of the chair and into a conventional vehicle seat. A number of safety issues arise when a wheelchair is used as a seat in a moving vehicle. Click on the following links to read about occupant restraint system safety and seating system safety. (Preliminary evaluation of wheelchair occupant restraint system usage in motor vehicles and Sling seating testing).
But the particular issue that we will address in this article is the safety of drop hooks. Drop hooks are devices made of aluminum or steel that attach the seating system to the frame of a wheelchair. Drop hooks are popular because they allow a user to quickly and easily remove the seat of his or her wheelchair so that the chair will fold up. But are these drop hooks safe? This article reviews the results of a study, conducted at the University of Pittsburgh’s Rehabilitation Engineering Research Center, that tested the ability of eleven commercially available types of drop hooks to withstand a crash.
Suppose you are a consumer and you buy a wheelchair with the “transport safe” label on it because you plan to sit in it while riding in moving vehicles. If the wheelchair is advertised as being transport safe, it has passed certain crash tests, specified by National and International wheelchair transportation safety standards (Homepage of Wheelchair Standards), that measure its ability to withstand a 30mph crash at 20g. If the chair passes the test, that means that the frame and the seating system attached to the frame both remained relatively intact throughout the crash.
But suppose you need a different seating system from the one that came with the chair. You replace the seat that was bolted to the wheelchair frame with one that you can attach or remove using a drop-hook. The chair, as a unit, is no longer guaranteed to be transport safe because the manufacturer did not test the wheelchair frame with the particular seating system you added. If your drop hook were to bend and deform during a crash, for example, your seating system might become unstable and severely compromise your safety.
This study examined the crashworthyness of eleven commercially available drop hooks in a simulated 30mph static crash test. The forces put on the chair and seating system mimicked forces that would be put on this equipment by the occupant of the wheelchair during a crash. A mock wheelchair frame and seating system, each designed to withstand multiple crash tests, were connected by each of the eleven hooks. A machine was then used to exert crash-like forces upon the wheelchair seat. To pass the test, a drop hook had to be able to withstand a force of 3750lb., which is the amount of force it would probably experience in a 30mph collision.
Unfortunately, none of the eleven drop hooks passed the test. All of the hooks deformed at less than half the 3750LB of force needed to pass the test. The hooks tended to bend so that they were no longer clamped securely to the wheelchair frame, causing the seat to become unstable. An unstable seat may cause the user’s occupant restraint system (seat belt) to rise above the hips and put large amounts of pressure on the vulnerable abdominal area. Hooks made of steel fared better than aluminum hooks, but no hook performed well enough to be deemed crashworthy.
The results seem to clearly indicate that the eleven drop hook types that were tested are not transport safe. However, there are some limitations to this study. First, the drop hook test was static, meaning that no actual motion was involved. Sometimes, dynamic tests that involve actual crash-like motion yield different results than do static tests. But dynamic tests are much more expensive and time-consuming, and the results of static tests are thought to be accurate enough to warrant their use in crashworthyness studies. But it is possible that some or all of the drop hooks would perform differently under more realistic crash-like conditions.
Secondly, the angles and stiffness of actual wheelchair seats and backs might cause there to be greater or lesser forces on the drop hook during a collision. But since no drop hook was able to withstand even half of the required 3750lb, it is safe to say that the hooks are still not strong enough, even with different seating system angles and stiffness.
Finally, this particular crash test only exerted downward forces on the mock wheelchair seat. In a real crash, a seating system would be subjected to forces that pull it along the frame in a horizontal direction, the so-called sheer forces. Sheer might cause a drop hook to perform more poorly than it did in this test, but poorer performance would not change the qualitative result of this study, (i.e. that none of the eleven drop hooks tested came close to passing the crashworthyness test).
The results of this study revealed that none of the eleven commercially available drop hooks tested in this study are transport safe. This means that wheelchair users who sit in their wheelchairs while in moving vehicles and who use drop hook attachment hardware to connect the frame and seating system of their wheelchairs should reconsider the safety of this practice. Future efforts should be directed toward developing safer drop hooks that can withstand crash forces up to 3750lb. Further research will also be directed at validating the practice of using economical static tests as a viable alternative to dynamic tests, so that consumers using static-tested wheelchairs and wheelchair components can be assured of their safety.
This summary is based on the following original article: Ha, D., Bertocci,G., Deemer, E., & . Karg, P. (2002).Evaluation of wheelchair sling seat and sling back crashworthiness. Medical Engineering and Physics, 24, 441-448.
Corresponding Author: DongRan Ha, MS, University of Pittsburgh, Department of Rehabilitation Science and Technology, 5055 Forbes Tower, Pittsburgh, PA 15260; firstname.lastname@example.org
Many wheelchair users, especially those with limited transferring ability, opt to sit directly in their wheelchairs while riding in moving vehicles. These wheelchair users can purchase wheelchairs that have passed certain crashworthiness tests devised by The American National Standards Institute, (ANSI) Rehabilitation Engineering and Assistive Technology Society of North America, (RESNA). If a wheelchair passes these crashworthiness tests, it has proven its ability to remain structurally sound in a severe frontal collision. It meets the ANSI/RESNA standards and can be sold and advertised as a “transport-safe” wheelchair.
But a wheelchair is not always bought as a complete unit off the shelf. Often, a consumer will buy the frame from a manufacturer and then outfit it with a seating system that is purchased separately. A safety problem can arise when this type of component system is used. Even when a complete, off-the-shelf wheelchair is tested and proves to be crashworthy, the ANSI/RESNA certification may be void if a different seating system is added. Seating system manufacturers do not yet have a way to test their products without attaching them to any number of wheelchairs to which they might some day be added. So manufacturers cannot market seating systems alone with a “transport-safe” label, and there is no guarantee that the seating system a consumer buys will be able to withstand the forces that it will experience in the event of a crash. For example, if a consumer buys a transport-safe wheelchair with a sling upholstery seating system but later needs to replace the seating system because it wears out, that consumer cannot be sure that the new seat he/she buys was tested for crashworthiness. This study attempted to develop a way of testing sling seats and backs without the expense and difficulty of combining every possible seat with every possible wheelchair frame.
Researchers at The University of Pittsburgh’s Rehabilitation Engineering Research Center on Wheelchair Transportation Safety designed a rigid metal structure that would serve as a mock wheelchair frame and could withstand multiple tests. To this frame, they attached and tested six different sling backs and six different sling seats. Two seats and backs were samples of the Sunrise Medical Quickie, two were samples of the Invacare 9000 XT, and two were samples of the Everest and Jennings P2 Plus.
When each sling back was attached to the frame, 2290 lbs of pressure was applied to it, so as to simulate the force that would be put on the seat back by the torso of the wheelchair occupant in a 30mph frontal collision. Each sling seat underwent a similar process, except that it had to withstand 3750 lbs of pressure. The level of force used to test the seats and backs were calculated based on the weight of an average male occupant, (187 lbs).
Four of the six backs and four of the six seats remained intact and were able to bear their respective loads for at least five seconds. The two seat backs that failed were both samples of the Everest and Jennings P2 Plus. The first sample failed at 1567 lb, and the second failed at 1787 lb.
One of the seats that failed was the Everest & Jennings P2 Plus seat, which failed at 3123 lbs. The other was one sample of the Invacare 9000 XT. The 9000 XT failed not because it could not bear 3750 lbs of force but because it could not remain intact for the full five seconds.
Most of the breakage occurred at the side seams, the points where the seats and backs attached to the frame of the chair. This finding implies that manufacturers of these products may improve those products’ safety ratings if they reinforce these areas.
While this study did reveal a lot of information about separately-purchased seating systems, there are a few important things to consider. First, this test was not dynamic. That is, it did not involve any crash-like motion. Therefore, the types of forces and the effects of those forces, which are sometimes very different in a dynamic environment than they were in this test, could only be approximated.
Secondly, the tests conducted in this study did not take into consideration the fact that, according to the ANSI/RESNA standards, seats should not deform downward beyond a certain point as they take the brunt of the crash forces. This is because if a seat deforms downward too much, the lap belt worn by the wheelchair user may rise too high and put large amounts of pressure on the vulnerable abdominal area. The seats tested in this study probably did sink down too far to meet the ANSI/RESNA standards. So even the seats and backs which were able to hold their loads for five seconds may deform beyond recommended levels.
Thirdly, the seats and backs were attached to the frame attachment hardware designed specifically for this test., So the results cannot account for failures due to regularly used hardware breakage. Along the same lines, the wheelchair frame used in this test was designed to be rigid so that it could withstand repeated crash simulations. However, real wheelchair frames are somewhat more flexible and therefore may contribute to failure of the seating system during a crash.
It is clear, then, that the results of a test such as this cannot be said to reveal a definitive yes or no answer as to the crashworthiness of a wheelchair seating system. It can, however, act as a cost-effective, easy to conduct, first screening for seating systems. After all, testing each seating system with any number of different wheelchair frames would be very expensive and time-consuming. These tests do suggest that currently available wheelchair seating systems may not be capable of withstanding crash-level forces. Manufacturers can use negative results of this test to further improve their products. We will continue to work to develop a more accurate yet economical means for testing seating systems so that manufacturers can adopt seating system standards and put tested, crashworthy seating systems on the market.
This summary is based on the following original article: VanRoosmalen, L., Bertocci, G., Hobson, D., & Karg, P. (2002). Preliminary evaluation of wheelchair occupant restraint system usage in motor vehicles. Journal of Rehabilitation Research and Development, 39, 83-93.
Many wheelchair users sit directly in their wheelchairs when riding in a motor vehicle. They rely on devices called Wheelchair Occupant Restraint Systems, (WORSs), to prevent them from sliding out of their chairs and becoming injured in the event of a crash. WORSs are lap and shoulder belts which secure the rider in much the same way modern car seatbelts function. Most WORSs are secured to anchors inside the vehicle itself and are not attached to the wheelchair.
This article reports on the results of a study that tested the use and satisfaction of vehicle-mounted WORSs in private cars, para-transit vehicles, and buses. Wheelchair users who travel with buses, para-transit and cars were asked to complete a survey.
The survey results revealed that WORS mounted in cars were quick, comfortable, and easy to use. However, similar systems found in para-transit vehicles and buses were frequently uncomfortable to wear, time-consuming to use, and hard to reach. The results of the study document the need for WORSs in para-transit vehicles and buses that are more comfortable and easier to use, so that people who use wheelchairs can travel more independently.
The National Highway Transportation Safety Administration has reported that if 85% of motor vehicle occupants wore seatbelts, 4100 lives per year would be saved, and 102,000 injuries per year would be prevented. In addition to being devices that keep the wheelchair from moving in a vehicle, WORSs, (the equivalents of seatbelts), are also crucial in making it safer for people to sit in their wheelchairs while riding in moving vehicles.
Despite the importance of WORSs as safety devices, results of this and other studies have found that 50 to 60% of people who sit in their wheelchairs while in vehicles do not use a WORS. Specifically, this study revealed that eleven out of eleven survey respondents chose at times not to wear WORSs on buses, and nine out of sixteen respondents sometimes chose not to wear a shoulder restraint in para-transit vehicles. It should be noted that para-transit riders are required to wear at least a lap restraint, so respondents could not have chosen to opt out of the lap restraint.
The survey revealed a host of reasons why WORSs installed in buses and para-transit vehicles are not often used. The belts may be too tight or dig into the users’ neck or shoulders. Securing a WORS often necessitates physical contact with the driver, who may or may not be trained to properly secure a WORS.
WORS are time-consuming to put on, and wheelchair users sometimes feel pressured not to take the time required, especially on a bus. Non-custom-fitted WORS might easily obstruct the wheelchair controls or the controls of an augmentative communication device installed on the wheelchair. Some WORSs on buses or para-transit vehicles are too hard to reach or simply do not work properly.
WORSs in privately-owned cars are often custom-installed. Custom-fitting the lap and shoulder belts allows for variations in body shape and size, wheelchair design, and positioning needs. It is clear, therefore, why many more people who use their wheelchairs in private cars wear WORSs. Only one out of fifteen survey respondents chose not to wear at least a lap restraint while in his/her privately-owned car.
Research that was conducted after the completion of this article examines the effectiveness of wheelchair-mounted WORS. WORS integrated directly into an individual’s wheelchair have the advantage of being custom-fitted, as well as being easier for many users to fasten independently. Because they fit better, they are also safer.
Note: To read more about integrated WORSs read the article (Wheelchair integrated occupant restraints: Feasibility in frontal impact) which is on the topic of WIRS
FIGURE 1: Pelvic belt crosses over the armrest of the wheelchair.
FIGURE 2: The WORS pelvic belt buckle is located high on the abdominal area of the individual. The upper torso restraint is located in a way that it does not touch the shoulder.
FIGURE 3. A failed attempt was made to install the pelvic and upper torso restraint on the individual using a power wheelchair equipped with a communication device, armrests and batteries.
Figure 4: Wheelchair with a vehicle mounted occupant restraint (left) and with a wheelchair integrated occupant restraint (right).
This summary is based on the following original article: VanRoosmalen, L., Bertocci, G., DongRan H., & Karg, P., (2001). Wheelchair integrated occupant restraints: Feasibility in frontal impact. Medical Engineering & Physics, 23, 687-98.
Department of Rehabilitation Science and Technology, Injury Risk Assessment and Prevention Laboratory, University of Pittsburgh, Pittsburgh, PA 15260, USA
Many wheelchair users sit directly in their wheelchairs when riding in a motor vehicle. They typically rely on devices called Wheelchair Occupant Restraint Systems, (WORSs), to prevent them from sliding out of their chairs and becoming injured in the event of a crash. WORSs are lap and shoulder belts that are anchored to the floor and frame of the vehicle. They secure the rider in much the same way modern car seatbelts function.
Previous research examined the effectiveness, comfort level, and usage rates of WORSs among people who sit in their wheelchairs while riding in privately-owned cars, buses, and para-transit vehicles. Click here to read an article reporting on that research. (Preliminary evaluation of wheelchair occupant restraint system) The survey revealed that WORSs installed in privately-owned cars were comfortable, fit properly, and had very high rates of usage. However, WORSs installed in buses and para-transit vehicles could not be custom-fitted to each individual rider. They were therefore hard to use, fit poorly, were uncomfortable to wear, and, as a result, were often not used by riders in wheelchairs.
The current study examines the feasibility and effectiveness of Wheelchair Integrated Restraint Systems, (WIRSs). These systems are built directly into an individual’s wheelchair, rather than being attached to the frame of the vehicle. WIRSs have some distinct advantages over vehicle mounted WORSs. First, they are custom-fitted, so they are much more likely to be comfortable and fit properly. Secondly, because they are integrated into the structure of the wheelchair, they are usually easier to reach and fasten. In some cases, this means that the person in the wheelchair is able to secure his/her lap and shoulder belts independently, rather than requiring assistance as he/she might have done when using a vehicle-mounted restraint system. Finally, because WIRS are more comfortable and easier to use than vehicle mounted WORSs, we expect that many more wheelchair users will buckle up when using WIRSs, greatly increasing their safety.
But are WIRSs and vehicle mounted WORSs equally effective in preventing injuries? Let’s imagine the ideal scenario, in which both the WIRS and the vehicle mounted WORS fit properly and have been fastened correctly.
The researchers at the University of Michigan’s Transportation Research Institute (UMTRI) tested both the WIRS and the vehicle mounted WORS, comparing their performance in a simulated frontal impact collision. To test the WIRS, the researchers placed a 187 LB human-shaped dummy that would simulate the weight of an average male passenger in the seat of a Tarsys wheelchair seating system with a reinforced steel frame. The frame was reenforced so that it could handle the force of the rider slamming forward into the lap and shoulder restraints in the event of a crash. The researchers simulated a collision occurring at a speed of 30 mph.
To test the vehicle mounted WORS, a non-modified Tarsys wheelchair seating system was used for the 30 mph simulated colision. In both tests, the Tarsys seating system was attached to a surrogate wheelchair base, one that can withstand multiple crash tests. A four-point tie-down system was used to secure the surrogate base to the test platform at four different places on the base’s frame.
The following variables were measured as the researchers compared the performance of the vehicle mounted WORS to that of the WIRS:
The test revealed the following results:
But what do those test results really mean? In short, the WIRS and vehicle mounted WORS performed about equally well in overall injury prevention, both systems meeting the automotive industry’s safety standards.
The reason that the head, neck, and knees moved farther forward when restrained by the WIRS was that the back of the wheelchair seat, to which the shoulder belt was attached, bent forward slightly as the weight of the dummy pulled at the restraint during the crash. As the seat back moved forward, so did the belt attached to it, allowing the head, chest, and knees to move as well. The wheelchair moved farther forward when a WIRS was integrated into it because, unlike with a vehicle mounted WORS, there was no vehicle frame to absorb some of the force of the collision. The only thing preventing the wheelchair from moving was the four-point tie-down system used to hold the chair itself to the vehicle. So the chair moved farther forward because there was no vehicle-mounted occupant restraint system holding it in place.
The fact that the head, chest, knees, and wheelchair all moved farther when the WIRS was used would seem to negatively affect the WIRS’s safety rating. But as the results described above indicate, the head, chest, and pelvis experienced less acceleration with the WIRS. This means that they moved a longer distance slowly, whereas they moved a shorter distance very quickly when the vehicle mounted WORS was used. This lower acceleration rate will contribute to an overall lower rate and severity of head injuries with the WIRS.
Less pressure was put on the dummy’s chest and breast bone when the WIRS was used because the back of the wheelchair bent slightly forward. This means that instead of the chest and breast bone absorbing all of the force of the crash, the back of the wheelchair absorbed some of the force, causing the chest and breast bone to be under less pressure.
Though the vehicle mounted WORS and WIRS have differing performance ratings for all of the variables measured, the researchers conclude that they are both safe and feasible restraint systems. But if a WIRS is to be integrated into a wheelchair and used safely, several important aspects of wheelchair design must be taken into consideration. First, the seat, seat back, and frame must be built to withstand the forces put on them in a crash. Secondly, to provide the best injury prevention, a WIRS should be integrated into the wheelchair as it is being built, not attached later. Finally, the back of a wheelchair outfitted with a WIRS needs to come up high enough to allow the shoulder belt to fit properly. Therefore, paraplegics, who often use wheelchairs with lower seat backs, may not wish to use chairs with WIRSs because they necessarily will have much higher seat backs. Paraplegics, however, can often transfer themselves out of their wheelchairs directly into the seat of a car, bus, or para-transit vehicle. So they are not usually the types of consumers for whom vehicle mounted WORSs and WIRSs were designed.
It is important to remember that the vehicle mounted WORS used for the study was fastened correctly and fit the test dummy well. In the real world, vehicle mounted WORSs do not usually fit comfortably, may not be properly maintained, or may not even be worn by the rider. We therefore expect that WIRSs will prove to be much safer than vehicle mounted WORSs in real life situations. Future research should be conducted to validate this theory. Research also needs to be conducted to obtain an appropriate set of strength standards that wheelchairs outfitted with WIRSs must meet.
Belt Fit Evaluation of Fixed Vehicle-Mounted Shoulder Restraint Anchor Across Mixed Occupant Populations
VanRoosmalen , L., Bertocci, G., Karg, P., & Young T. (1998). Belt fit evaluation of fixed vehicle-mounted shoulder restraint anchor across mixed occupant populations. Proceedings of the RESNA annual conference, Minneapolis, 40-43.
Department of Rehabilitation Science and Technology, Injury Risk Assessment and Prevention Laboratory, University of Pittsburgh, Pittsburgh, PA 15260, USA
Wheelchair Tiedown and Occupant Restraint Systems (WTORS):
Many wheelchair users, especially those with limited transferring ability, opt to sit directly in their wheelchairs while riding in moving vehicles. Two kinds of safety systems protect the user in the event of a crash. The first system is the wheelchair securement system. Often taking the form of 4 tiedown straps, the securement system anchors the wheelchair to the floor of the vehicle so that it will not move while the vehicle is moving. The second safety system is called an occupant restraint system. Its job is to restrain not the wheelchair but the person in the wheelchair. It functions much like a conventional seatbelt.
Most wheelchair occupant restraint systems, (WORSs), are anchored to the floor and sides of the vehicle. This system works well in privately-owned cars because a WORS can be specifically designed to fit the body type and chair height of the user.
All WORSs must pass certain tests that measure their ability to prevent injury in a 30 mph crash. The tests are conducted using a 187 lb test dummy that represents the size of an average man. WORSs in para-transit vehicles and buses are used by many people with many body types and wheelchair seat heights, so they cannot be custom-fitted and are therefore designed to fit a 187 lb person. This article examines the injury reducing capabilities of non-custom-fitted shoulder belts for people smaller than 187 lbs.
To test injury prevention for a smaller person, researchers at The University of Pittsburgh’s Rehabilitation Engineering Research Center on Wheelchair Transportation Safety set up a mock wheelchair station with a restraint system that mirrored a vehicle-mounted WORS. A six-year-old child and an adult woman representative of the smallest 5 % of the female population each sat in a wheelchair that was fitted to their size and were restrained by a vehicle mounted shoulder and lap restraint. Measurements were then taken of the angle of the belt across the body and of the belt height on the body.
According to occupant restraint standards designed by the Society of Automotive Engineers, belt height and belt angle must both be within certain ranges in order for the belt to provide optimal crash protection. The belt must be high enough to prevent the shoulder from rotating out of the belt and moving forward, but not so high that it cuts across the vulnerable neck and throat area, potentially causing injury to the neck in the event of a crash. The belt angle must be between 50 and 60 degrees.
After measurements of belt height and angle for the two test subjects were taken, the RERC researchers determined that, for these smaller than average individuals, injury protection is compromised. But even average-sized individuals may not be optimally protected in buses and para-transit vehicles. This is because wheelchair seat heights vary greatly. So if, for example, a 187 lb man is using a wheelchair that is low enough for his feet to touch the ground, the shoulder belt will come up too high on his neck for optimal protection, and he may be injured in the event of a crash.
Unlike conventional car shoulder belts, which are frequently adjustable, WORS in para-transit vehicles and buses are anchored to set points on the vehicle and cannot be changed, causing belt height and angle to be fixed. So what should you do if you are much smaller or larger than average or have a very tall or very short wheelchair but still want to be able to use a safe occupant restraint system? An option currently under investigation by the RERC researchers is a restraint system that is built directly into the wheelchair. These lap and shoulder belts can be custom-fitted and thus provide better injury protection than an ill-fitting restraint system that is mounted in a bus or para-transit van.
Linda van Roosmalen PhD, Gina E. Bertocci PhD
University of Pittsburgh, Injury Risk Assessment and Prevention Laboratory, Department of Rehabilitation Science and Technology, Pittsburgh, PA, USA
Many wheelchair users sit directly in their wheelchairs when riding in motor vehicles. Often, this is because they have little or no ability to transfer out of the chair and into a conventional vehicle seat. A number of safety issues arise when a wheelchair is used as a seat in a moving vehicle. The main difficulty with using a wheeled mobility device as a seat in a motor vehicle is that most wheelchairs are not designed to be able to handle the forces put on them in the event that the vehicle crashes. A variety of wheelchair components are very susceptible to damage when crash forces are put on them, and this damage can easily result in injury to the wheelchair user.
One set of wheelchair components that are susceptible to failure during a crash are the casters or front wheels of the wheelchair. During a frontal impact, the wheelchair and its occupant rotate forward with a great deal of force, and much of that vertical and horizontal force is applied to the casters, potentially causing buckling or cracking of the components. This study examined different types of scenarios and wheelchair set-ups to test the varying levels of force they place on the front wheelchair casters.
Researchers at the University of Pittsburgh and the University of Michigan ran eight dynamic crash tests. This means that each test simulated actual crash-like movement and forces. Each test simulated a collision at 30 mph at 20g. A surrogate wheelchair base was used which simulated a commercial wheelchair base but was designed to withstand multiple crash tests.
Eight different scenarios were tested, with each test using different combinations of seats, backs, and points at which the wheelchair was secured to the mock vehicle floor. Each time, a test dummy representing the size and weight of an average-sized man was placed in the wheelchair to simulate the wheelchair user. The different seats, backs, and securement point hights placed varying levels of vertical and horizontal forces on the front wheelchair casters. Devices called ‘load cells’ were placed under the caster wheels to measure this varying amount of force during each crash test.
The average amount of vertical force placed on caster assemblies was 4738 newtons (N), and the average horizontal force was 1343 (N). The highest amount of vertical force was measured to be 7209 (N). This resulted from a combination of a high rear securement point and a failure (cracking, bending or buckling) of the seating system. Because the seating system was unable to withstand the forces put on it by the test dummy during the crash test, the caster assemblies took the brunt of the impact, causing the amount of force put on them to be very great. Low rear securement points also caused high levels of force on the casters, (5824 (N)). This is because, since the point of securement was far below the wheelchair’s center of gravity, the wheelchair and test dummy rotated, again causing the casters to take the brunt of the impact.
What we can learn from these tests is that a strong seating system that is able to withstand crash forces is crucially important to maintaining the integrity of the casters. In addition, a rear securement point located at the wheelchairs’ center of gravity (bulk of the wheelchair) is the best place to attach wheelchair tiedown straps. Finally, since casters must be able to handle some amount of force despite a strong seating system and appropriately-placed securement points, it is best if casters are able to deform in a controlled manner during a crash. This controlled deformation will allow the caster assemblies to absorb some of the energy released in the collision without rendering the wheelchair unstable and putting the wheelchair user more at risk.
The results of this study reveal that seating system failure and high or low rear securement attachment points put wheelchair casters more at risk for failure since the forces put on them are greatest under those conditions. Not only should casters be built to handle crash-like forces in a controlled manner, but it is essential that other components of the wheeled mobility system such as the seating system also should be designed with collision safety in mind. A wheelchair user’s best option would be a wheelchair that has been crash tested according to the American National Standards Institute/Rehabilitation Engineering and Assistive Technology Society of North America, (ANSI/RESNA), standard WC19, a voluntary standard that dictates the types of rigorous crash testing a wheelchair should undergo before it can be said to be safely used as a motor vehicle seat. Such wheelchairs are labeled “transport safe” or “transit safe”, and have passed similar tests to the ones administered in this study. Future research needs to be directed toward the further development of such wheelchairs, seating systems and wheelchair components.
Linda van Roosmalen Ph.D.1; Gina E. Bertocci Ph.D.1; Donald Herring, IDSA. 2.
1University of Pittsburgh, Dept. of Rehabilitation Science and Technology, Pittsburgh, PA, USA 2 Arizona State University, College of Architecture & Environmental Design, Phoenix, AZ, USA
Many wheelchair users, because of the extent of their mobility impairments, must remain seated in their wheelchairs while riding in motor vehicles instead of transferring to a normal vehicle seat. Wheelchairs are not designed to be used as motor vehicle seats, so a number of safety concerns arise. The main concern is that the wheelchair user may become injured in the event that the vehicle is involved in a collision or the driver must turn or stop very suddenly.
Wheelchair securement systems, (devices that anchor the wheelchair to the vehicle floor), and occupant restraint systems, (seatbelts for wheelchair users), have been designed to address these injury concerns. However, these securement and restraint systems are difficult to use, and they are often either used improperly or not used at all. The current study investigates the response of wheelchair-seated passengers on large, fixed route transit buses to sudden braking and turning.
This study focuses on large, fixed route buses rather than smaller vehicles because the types and amounts of crash-related forces experienced by passengers in larger buses are much less than those felt by occupants of smaller vehicles, and this study is aimed at examining these smaller so-called ‘G-forces’. In fact, there have been very few documented injuries to wheelchair-seated bus passengers resulting from actual crashes. Most injuries to wheelchair users riding the bus seem to result from the more day-to-day sudden braking and turning that bus drivers do. Quick stops and starts can easily result in an improperly secured wheelchair tipping and the unrestrained wheelchair user falling and becoming injured.
Therefore, some have argued that the highly crash-tested but cumbersome securement and restraint systems necessary in vans and cars may not be necessary in fixed route buses since collisions are not nearly such a concern as sudden braking and turning. The aim of this study is to work toward determining whether securement and restraint systems that are less able to prevent injuries due to crashes but easier to use are, in fact, safer for wheelchair-seated bus passengers. In other words, if these systems are easier to use and still protect bus-riding wheelchair users from injury caused by sudden braking and turning, more people may be likely to use them, causing an overall increase in injury prevention among wheelchair users.
The researchers used a computer model simulation to examine the dynamic response of a wheelchair-seated bus passenger experiencing a low-G, low impact event such as a sudden stop or turn. Three different scenarios were tested. In one scenario, the occupant was using a four-point tiedown system but no occupant restraint system. In the next scenario, the occupant used a two-point securement system, (in contrast to the recommended four-point securement system), and no restraint system. In the third scenario, the occupant used a two-point securement system and a pelvic occupant restraint. The simulated turn occurred at 20 mph, and the turn itself had a radius of 50 feet. Bus passengers would feel a force of .35 to .6 g during this turn. The simulated sudden brake maneuver had a deceleration of twenty to zero miles per hour at .5 to .71 g (See Figure 1). The wheelchair being tested was a 34-pound manual wheelchair with a test dummy representing the size of an average male, (168 lbs.), seated in the wheelchair.
In the first scenario, where a four-point tiedown but no occupant restraint was used, the occupant was ejected from the wheelchair during sudden braking, and the torso and/or head of the occupant impacted the wall of the vehicle and/or armrest during the sudden turn. When friction between the seat and the occupant’s legs was increased, the torso and lower body was delayed in sliding out of the chair during braking, but the head moved farther forward at greater speed, a scenario which would likely cause injury to the head in a real sudden braking maneuver. Increased seat friction did not significantly impact the motion of the occupant during the sudden turn (See Figure 2).
Figure 2: Left: 20mph/0.7g braking at 1200ms. Right: 20mph/0.6g turning at 1200ms.
In scenario 2, where a two-point tiedown and no occupant restraint was used, the sudden braking maneuver resulted in similar events as when the four-point tiedown was used, (occupant sliding from the chair and probable head injury). The two-point tiedown was constructed so that the front and rear tiedown straps were on the same side of the wheelchair. When the sudden turn occurred in the same direction as the two tiedowns, the wheelchair tipped easily, likely causing injury to the occupant as he/she impacted the vehicle floor or wall (See Figure 3). If a vehicle wall were placed on the same side of the chair as the location of the tiedown straps, the wheelchair would not tip, but the occupant would still likely hit the non-energy-absorbing wall, probably causing injury as well. When the turn occurred in the opposite direction as the tiedowns, the chair did not tip, but the turn occurred with enough force that the occupant rotated over the armrest of the chair and stood a substantial risk of falling sideways out of the wheelchair, again causing injury (See Figure 4).
In scenario 3, where a two-point tiedown and pelvic restraint were used, the occupant was not ejected from the chair during braking. When the sudden turn occurred on the opposite side of the chair from the two tiedowns, the occupant still rotated over the armrest but did so to a lesser degree than when no pelvic restraint was used.
It is important to remember that this was only a computer-simulated model. The model wheelchair and occupant set-up used in this simulation have not been validated for the turning and braking simulations used in this study but rather only for a 20g frontal impact collision. So the results should be interpreted with caution. Emergency maneuvering tests run using real forces, wheelchairs and test dummies are the next important step in fully validating these results.
This study has investigated wheelchair and occupant responses to emergency braking and turning in large transit vehicles. Our preliminary findings suggest that unsecured forward facing wheelchairs and unbelted occupants may not be safe even in non-crash conditions. Preliminary results indicate that the addition of the pelvic restraint improved the overall response of the occupant during braking and to a lesser extent during turning. Our findings support anecdotal reports of wheelchair accidents occurring during normal or emergency driving. Furthermore, our study points to the need for 4 wheelchair tiedowns and occupant restraints under forward facing driving conditions.