Do what you want:
Making Access accessible
Nick Tyler
Accessibility Research Group
UCL
Medical Model – fix a condition
• Cannot
walk
Medical
condition
Treatment
• Prescribe
Wheelchair
• Can move
Solution
Social Model – fix the environment
• Cannot
climb kerb
Environmental
condition
Treatment
• Lower
kerb
• Can climb
kerb
Solution
Person
• Activity
– What do you want to do?
• Environment
– Where do you want to go?
• Person
– What can you do?
Capabilities Model – fix the
interactions
• Requires
Capabilities
Activity
Environment
• Requires
Capabilities
• Provides
Capabilities
Person
Solution
• If Provided
≥ Required
Gaps
• London Underground
Bank (Central Line)
(1992 Rolling stock)
12
Stratford (Central Line)
(1992 Rolling stock)
Experiment
13
Experiment
14
The accessibility question
• For society to be equitable, everyone must be
able to achieve their desired activities
• This often requires movement
• Movement requires accessibility
• Accessibility depends on the relationship
between Required and Provided Capabilities
• How do we compare these Capabilities?
The study of Accessibility
Challenges
1. Large number of variables
2. Variation across the
population
3. Variation within the
individual
4. Coping strategies
5. Co-morbidity
6. Multiple inputs leading to
single – but highly
differentiable – output
Responses
1. Must not average variables
away
2. Values and distribution
3. Measure of performance
4. Need to look at core efforts
as well as outputs
5. How is co-morbidity
managed?
6. Rather like weather
systems
Why do we fall over?
• Falls are a big problem
– Only a tiny fraction of incidents are presented in
hospital
– Costs immense but hidden (upper femur fracture
costs the NHS ~£1.5bn/year)
– Psychological issue probably greater than the
physical problems
– Affects older people a lot
– So why does a fall occur?
Neurological
capability
Sensory
capability
300-500 msec
Perceive the obstacle
The brain recognises the
obstacle and instructs
the eyes to look out for
the potential danger
Cognitive/
physiological
capability
Physical
capability
Lift the leg
Calculate the required
movement and the correct
physiological stimulus for the
movement … recalculate and
adjust them during the
approach
2-3 sec
The obstacle
So why don’t we fall over all the time?
• How many steps per stumble?
• We make 10,000 steps per day so the special
ingredient for a fall is a very rare and highly
changeable beast
• Starting from the model just described, we
can see that a lot of things precede the
encounter with an obstacle and we are now
looking to see if we can begin to understand
these.
Eyes
2
1
4
4
7
5
3
6
6 frames showing eye fixations on a distant object – Frame 7
shows that the eye has moved. Each frame lasts 40 millisec so
the fixation was for 240 millisec – i.e. about a quarter of a
second.
We know that the eye first fixates on an obstacle such as a
kerb when the person is about 3m away from it and then
re-fixates several time before arrival.
Why does the eye fixate the first time?
Interaction between eyes and the
environment
What happens in the pedestrian
environment?
Where to begin?
• We started by looking at the outputs:
– Kerb heights
– Gradients
– Walking speed
• But it soon became clear that this approach
would not be sufficient for developing better
outcomes
Footways & Crossfalls
• Footways allow people to
access services and other
transport options
• Crossfalls are present to aid
water drainage from
footways
• There is agreement
worldwide that 2.0% to
2.5% gradient is acceptable
for wheelchair users
2%
Example – pushing a wheelchair
The Capability Model in detail
Attendant-Propelled Wheelchair System
(APWS)
User
(Attendant)
Self-Propelled Wheelchair System
(SPWS)
User
Wheelchair
(occupant)
Activity
Environment
Capabilities Key
Required capabilities
Provided capabilities
Fixed Capabilities
Task
Self-Propulsion
RESULTS
Results of crossfall experiments
Most people could:
• Start the wheelchair
• Push the wheelchair in a straight line
• Stop the wheelchair
But…what required capabilities did it require?
Start Forces
Independent Variable
0%
2.5%
4%
Downslope Start Ft [N]
72.08
65.84
69.78
Downslope Start Push Time [s]
.995
.960
.930
Upslope Start Ft [N]
63.49
52.42
50.74
Upslope Start Push Time [s]
.950
.840
.895
Stop Forces
Independent Variable
0%
2.5%
4%
Downslope Stop Ft [N]
-42.37
-38.31
-40.02
1.94
1.92
1.65
-56.14
-62.12
-61.74
1.97
2.50
2.57
Downslope Stop Push Time [s]
Upslope Stop Ft [N]
Upslope Stop Push Time [s]
Attendant-Propulsion
RESULTS
Results of attendant experiments
All people could:
• Start the wheelchair
• Push the wheelchair in a straight line
• Stop the wheelchair
But…what required capabilities did it require?
Increase in crossfall means people apply a difference of force when starting
Increase in crossfall means people apply a difference of force when stopping
No change in sum of force used by attendants
Increase in difference of force used by attendants
Guidelines taken from Snook & Ciriello 1991
Conclusions
• Crossfalls introduce a second capability – the
control of different forces in each arm
• This second capability may be the limiting
factor in the gradient attendants can push
successfully along
• Required force could exceed legal maximum
Capabilities and Accessibility
Provided Capabilities
Required Capabilities
If Provided Capabilities overcome Required Capabilities, then it should be accessible
…