Human factors of braking

Dean Southall
Ergonomist

Dean Southall Consultancy
Bringing the car to a halt
Getting on the brake
 Applying efforts
 Controlling the stop
 When it all goes wrong

Moving the foot to the brake pedal

mean brake perception-reaction times of 1.5s

but affected by: time to collision
expected or unexpected (+0.2s)
pedal geometry
whether road or track (road faster)
not age of driver
Applying efforts
How much force can a driver apply to the pedal?
Estimated ….
5%ile male = 800N,
5%ile female = 450N….
but….
how old is the driver?
what is the pedal geometry?
who’s car are they driving?
Controlling the stop
Brake feel and vehicle control.
The lower limit to gain is set by the weakest
driver’s strength.
The upper limit to sensitivity or gain is set by
controllability.
Controllability = Driver perception of the
relationship between their input and the braking
system response.
Hair cells to judge deceleration
Visual information (optic flow) used to judge
TTC and assess deceleration.
Assess current effort applied to pedal and
adjust.
Ability to adjust depends on system
gain/sensitivity.
Should not be greater than driver’s threshold
for sensing differences in muscle effort.
Loss of lateral control is worse at higher gains:
(Mortimer and Olsen, 1971)
Mean no of trials with loss of control
20
15
10
5
0
0.065
0.037
0.021
0.012
0.007
Deceleration/pedal force gain (g/lb.)
0.004

Pedals with travel resulted in fewer wheel lockups.
Vehicle control problems for emergency
braking
pedal becomes isometric so less feedback
for driver
driver at limit of effort so muscle control
reduced.


Hence ABS
When it all goes wrong

Case study: unintended acceleration
accidents.
 Scenario
- automatic vehicle
- - slow speed manoeuvre
- - driver applies brakes but vehicle moves
forward
- driver applies more braking effort and
vehicle moves faster!
- vehicle only stops following collision
Reason – pedal confusion!
Why did driver press wrong pedal?
Only two pedals
Body twist
Similar pedal design
Pedal bay layout
(e.g. wheel arch)
Why did driver continue to
press wrong pedal
Efference copy
The brain ‘knows’ where the foot is
because it sent the movement message
Need for strong feedback to correct this
assumption
Why they don’t try other
actions
Incidents can last long enough for the
driver to take other actions…
–Switch off engine
–Put into neutral
–Apply handbrake
The flight or fight response
Sudden startling stimulus

High risk of danger

Action available

Action required immediately

HYPERVIGILANCE
The hypervigilant state

Focus of attention on one activity

Awareness of sensory feedback restricted

Cannot divide attention

Information processing disrupted
Hypervigilance and vehicle
control

Incoming powerful stimuli (noise, view
ahead) override any pedal error feedback
from pedal

Driver attends to steering - no processing
capacity to ‘work out’ what has happened

No processing capacity to select other actions
Preventative measures

pedal design
 interlocks
 training
Hungry yet?
Thank you for listening