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Usability Study of a Powered Lift for Wheelchair Users
Mahiyar F. Nasarwanji (1), Victor L. Paquet (1), David J. Feathers (2), James A. Lenker (2)
(1) Department of Industrial and Systems Engineering, University at Buffalo, The State University of
New York, Buffalo, New York
(2) Department of Rehabilitation Science, University at Buffalo, The State University of New York,
Buffalo, New York
Stairways into building or public vehicles are important environmental barriers that limit
accessibility to users of wheeled mobility devices. Powered van lifts can serve as an alternative
to stairs, ramps or porch lifts, but they have not yet been carefully evaluated for this purpose.
The objectives of this study were to characterize the usability of a powered van lift device for
wheelchair users and demonstrate the utility of using a multi-method evaluation approach to
identify opportunities for design improvements. Twenty experienced wheeled mobility device
users either alone (n=11) or with the assistance of a caregiver (n=9) completed tasks using a
powered van lift. Measurements were made on the unrestricted space required to enter and exit
the lift, time required to enter and exit the lift, errors made during the operation of the lift’s
control, and self-reports of device usability obtained with a questionnaire. Results indicated that
the clear space required for the lift was less than what would be expected for a ramp and that the
self-reported usability of the device was reasonably good. However, the time required to use the
lift was high and participants had difficulty operating the lift’s safety-belt. Improvements should
be made to the design of the safety-belt to increase usability. Additional studies that include
other user populations are recommended to investigate the efficacy of the device as an alternative
to stairs, ramps and “porch” lifts.
INTRODUCTION
Approximately 1.7 million individuals in the United
States use wheelchairs or scooters (Kaye, Kang, &
LaPlante, 2000), with increasing prevalence expected in
the near future. Stairways into buildings or public
vehicles are among the most challenging environmental
barriers for users of wheeled mobility devices (WMD)
including manual wheelchairs, power chairs and
scooters.
One alternative to stairs or ramps is a powered lift.
Wheelchair van lifts have been widely used when the
distance to be traversed is large as in the case of private
and public vans where a ramp would not be feasible. It
may also be possible to adapt van lifts as an alternative
to stairways and more expensive “porch” lifts used in
buildings.
Lifts may also have applications in the area of
universal design by also benefiting those who do not use
wheeled mobility devices. For example, older adults,
adults requiring walking aids, children, and others could
potentially benefit from lifts that allow access to private
housing or public transportation.
However, anecdotal reports indicate that the use of
lifts for vehicle entrance and exit remains difficult, and
the use of van lifts in private housing is rarely, if ever,
employed, perhaps because there has been little
attention given to the usability of such devices.
While this study does not attempt to address all
issues of usability for all potential user groups, it
attempts to uncover key usability issues that impact the
usability of a powered lift for the primary user group –
wheelchair users. There were two study objectives:
1. To characterize the usability of a powered lift
device for wheelchair users
2. Demonstrate the utility of using a multi-method
evaluation approach to identify lift design deficiencies.
METHOD
Equipment
Lift & Platform. The lift selected for the evaluation
was a wheelchair van lift developed for use in vans and
busses. The lift was similar to a cantilever with a 1.3m x
0.9m elevating platform.
The occupant would board the lift at ground level
and would exit the lift at 0.46m above ground level onto
a stable, enclosed wooden platform (1.5m x 1.5m). The
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lift extended 2.3m from the edge of the platform when at
ground level (unfolded and down) and 0.43m from the
edge of the platform when positioned on top of platform
and completely folded. All lift operations were
controlled by a pendant tethered to the lift with an on/off
rocker switch and four push buttons that unfold (deploy)
the lift, fold (stow) the lift, raise the lift (up) and lower
the lift (down). The lift had hand rails, a safety-belt to
secure the occupant, and a front and rear roll-stop to
prevent users rolling off the lift.
Video. Three cameras were used to video record
each trial. One camera was aimed vertically downward
from the ceiling and provided video used to estimate the
floor space required to enter and to exit the lift. The
second camera was positioned to provide an oblique
view from the front of the lift to capture general task
performance. A handheld camera was also used to
capture close up, the participant’s hand activity when
using the controls and when adjusting the seatbelt.
Participants
Twenty experienced WMD users (mean age=50.8
years; range=26-83 years) were recruited. Sixteen had
ten years or more of experience using van lifts. Most
(n=18) used van lifts at least a few times per week.
Nine WMD users had caregivers (mean age=53.3
years, range=32-73 years) who assisted with securing
the safety-belt on the lift and operating the controls.
Most of the WMD users who participated with
caregivers used power chairs (n=8); those who were
alone were a mix of manual chair users (n=7) and power
chair users (n=4). Participants were paid an honorarium
of $50.
Procedure
WMD users and caregivers were instructed to use
the lift as they would normally, either as a team or
alone. Participants were required to complete 5 tasks:
1. Deploy. Operate controls that bring the lift and
lower it to ground level.
2. Enter. Approach the lift at 900 to the lift, back the
wheelchair onto the lift and fasten the seatbelt. From the
raised platform, the participant boarded the lift facing
forward.
3. Go up / down. Operate the controls to travel from
the floor to the platform or vice versa.
4. Exit. Back the wheelchair off the lift onto the
platform, or unbuckle the seatbelt, exited the lift onto
the floor and performed a 900 turn.
5. Stow. Participant folded the lift completely
Participants completed 5 cycles of the above tasks.
The first 2 cycles were trial runs that allowed
participants to become acquainted with the lift. During
these trials, the investigators provided instructions as
needed for using this particular lift. The remaining 3
trials were videotaped.
If the WMD user was alone (no caregiver), the
control box was handed to him/her at the appropriate
time during the trial. If a caregiver was present, the
controls were attached to the platform at a height of
1.3m from the ground and were operated by the
caregiver.
After the 5 runs, all participants completed a
usability survey. Survey items addressed a variety of
usability domains, including setup, safety, time taken,
mistakes made, information needs, physical and mental
effort, approach, use of controls and seatbelt, and level
of assistance required. Participants responded to each
item on a five point Likert scale that ranged from
strongly disagree to strongly agree. Investigators noted
any additional comments made by participants.
Performance measures and analysis
Performance measures included the following:
1. Unrestricted space required to enter and exit the
lift from the ground. In order to access space
requirements for use of the lift a 2.4m x2.4m grid was
created on the ground in front of the lift when unfolded
and down. Individual grid squares were 0.3m x
0.3m.The number and locations of squares on the grid
that a participant occupied when boarding or exiting the
lift was assessed via video analysis of the recordings
made with the ceiling mounted camera. Two researchers
observed the video and identified the area used on the
floor. Reliability between observers for floor space
requirements was high. For those cases in which there
were discrepancies in the required floor area, the
observers re-reviewed the video recordings and came to
agreement.
2. Required time to enter and exit the lift. Time for
each task was calculated from the time stamp on the
video recordings. T-tests were used to evaluate
differences in task time between participants with
caregivers and those without givers and based on chair
use (manual vs. power chairs).
3. Errors made during the operation of the lift’s
control. Video was coded for each trial for the sequence
of buttons pressed and if there was hesitation, assistance
required and if an incorrect button was pressed.
4. Self-reports of device usability obtained with a
questionnaire. The responses from each statement were
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coded on a scale of 1 to 5; with a higher score indicating
better usability. Median values for WMD users and
caregivers are reported.
RESULTS
Space requirements
Approximately 5 sq. m. of clear floor space area was
needed to accommodate all of the participants in this
study (Figure 1). A majority of the WMD users
required at least 1.5 m of clear floor space in front of the
lift when maneuvering onto the lift.
0.3 0.3 0.1 0.1
0.9 0.9 1.0 1.0 1.0 0.8 0.4 0.2
1.0 1.0 1.0 1.0 1.0 0.9 0.6 0.2
0.7 0.8 0.9 1.0 1.0 0.9 0.7 0.3
0.4 0.4 0.6 0.8 0.9 0.9 0.6 0.2
0.0 0.1 0.2 0.5 0.6 0.5 0.3 0.1
0.0 0.0 0.1 0.2 0.2 0.2 0.2 0.1
0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
LIFT
Figure 1: Left: Direction of movement when entering the
lift. Right: Probability that a particular section of the
floor was required by the 20 wheeled mobility device users
(each square represents 0.3 sq. m).
0.3 0.3 0.1 0.1
0.5 0.6 1.0 1.0 1.0 0.4 0.3 0.2
0.8 0.9 1.0 1.0 1.0 0.4 0.3 0.2
1.0 1.0 1.0 1.0 0.9 0.4 0.3 0.2
0.7 0.8 0.8 0.8 0.4 0.3 0.2 0.1
0.3 0.4 0.3 0.3 0.2 0.1 0.1 0.1
0.1 0.1 0.1 0.1 0.1 0.1 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
LIFT
Figure 2: Left: Direction of movement when exiting the
lift. Right: Probability that a particular section of the
floor was required by the 20 wheeled mobility device users
(each square represents 0.3 sq. m).
When exiting the lift onto the floor, the path of
movement was more variable but the required floor
space was less than that required when entering the lift
(Figure 2).
Task time
There was a significant difference in time (p=0.002)
between participants having caregivers and those not
having caregivers. On average, those without caregivers
required 140 s more than those with caregivers (Figure
3). There was also a significant difference (p=0.03)
between manual and power chair users. On average
manual chair users required 119 s more than power chair
users (Figure 4).
Manipulating the safety belt required a large
proportion of the time for both entering (48%) and
exiting (45%) the lift. Overall task time could be
dramatically reduced if time taken to fasten the safety-
belt could be reduced.
Figure 3: Total time taken to complete one cycle (from the
ground to the platform and back) based on presence of
caregiver (- - -: group mean).
Figure 4: Total time taken to complete one cycle (from
ground to the platform and back) by wheelchair type (- - -:
group mean).
Errors during control use
The number of errors was very small compared to
the number of trials. The probably of making an error
was 0.17 for all three errors types combined. The two
main errors while using the controls were hesitation
where the participant was not sure which button to press
and pressing the wrong button. Errors were made
between the pairs of buttons, stow and up, and deploy
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and down were the most common. Four participants
mentioned that the placement of the buttons were a
cause for confusion. One recommended the need for
simpler terminology to replace “stow” and “deploy”.
Others suggested that the controls should not be tethered
to the lift and that the on/off button should be larger.
Self reports of usability
In spite of the large amount of time required to use
the lift, participants did not feel the lift took more time
than it should (median value 4.5). The lift was easier to
use than to similar lifts used for public transportation
(WMD users median value: 3.5; caregiver median value:
3) and private transportation (WMD users median
value:4; caregiver median value: 4).
Participants reported that setting up, approaching
and wheeling on and off the lift was easy. Scale scores
suggested that the lift required minimal mental effort
and physical effort and did not pose a significant safety
risk, each having a median value of 5.
The participants reported that the controls were easy
to use and understand. WMD users recommended an
additional set of controls to be installed on the lift.
Participants also reported that use of the lift
provided the relevant information needed to complete
the task. However, over half of the wheelchair users
(n=12) and 3 caregiver reported that they made errors
while using the lift. These errors were associated with
the use of the controls and task of backing up onto the
lift. Five WMD users reported difficulty looking back
when entering the lift backwards.
Eleven participants indicated that they required
some assistance while using the lift and 6 felt using the
lift would draw unwanted attention to them.
DISCUSSION
This study tested the usability of a wheelchair van
lift using a multi-method approach. The results indicate
that participants believed that lift was easy to use,
although other analyses demonstrated that use of the lift
required lots of time and that errors were sometimes
made during use.
One advantage of a powered lift over a ramp is the
potential space savings. For a rise of 0.45m, 5.5m of
floor space is needed for an appropriate ramp. This is
two times greater than that required of the lift tested in
this study. In addition, the lift can be stowed to reduce
its footprint to nearly zero when not in use. The lift
might be useful in a built environment such as homes
where space is limited.
However, unless improvements are made to the
device, it is likely that alternatives to stairs such as
ramps will be preferred over the powered lift. Based on
estimates of the time it takes WMD users to traverse
ramps (1.25 s for every 3.65 m traversed (US Access
Board, 1996)), use of the lift would require significantly
more time for the conditions tested in this study.
The video-based data and the self reports of
usability suggest that modifications to the seatbelt are
needed. This seatbelt required buckling from the side
and individuals often had difficulty positioning the
harness. Improvements to the design of the buckle or
harness could lead to dramatic reductions in the time
required for entering and exiting the lift.
The multi-method usability evaluation approach
used in this study proved to be very beneficial. Without
multiple data sources it would have been impossible to
identify the problems with the usability of the lift’s
seatbelt and clear floor space required to enter and exit
the lift. Additional research involving a wider range of
users is needed to investigate the potential of a powered
lift to serve as a universal design alternative to stairs or
ramps.
ACKNOWLEDGEMENTS
Natalie Song and Bernice D’Souza are
acknowledged for their efforts in the analysis of the
video recordings used in this study.
This paper was developed with funding from the
U.S. Department of Education, National Institute of
Disability and Rehabilitation Research, Contract No.
H133E050004-07. The contents of this report do not
necessarily reflect the views of the U.S. Department of
Education.
REFERENCES
Kaye, H. S., Kang, T., & LaPlante, M. P. (2000).
Mobility Device Use in the United States. Disability
Statistics Report 14: University of California.
(Disability Statistics Center)
US Access Board. (1996). A review of technical
requirements for ramps: North Carolina State
University)
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