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Human factors of brakingHuman factors of braking
Dean SouthallDean Southall Ergonomist Ergonomist
Dean Southall ConsultancyDean Southall Consultancy
Bringing the car to a haltBringing the car to a halt
Getting on the brakeGetting on the brake Applying effortsApplying efforts Controlling the stopControlling the stop When it all goes wrongWhen it all goes wrong
Moving the foot to the brake pedalMoving the foot to the brake pedal
mean brake perception-reaction times of mean brake perception-reaction times of 1.5s1.5s
but affected by: -but affected by: -
time to collisiontime to collision
expected or unexpected (+0.2s)expected or unexpected (+0.2s)
pedal geometrypedal geometry
whether road or track (road faster)whether road or track (road faster)
not age of drivernot age of driver
Applying effortsApplying efforts
How much force can a driver apply to the How much force can a driver apply to the pedal?pedal?
Estimated ….Estimated …. 5%ile male = 800N, 5%ile male = 800N,
5%ile female = 450N….5%ile female = 450N….
but….but….
how old is the driver?how old is the driver?
what is the pedal geometry?what is the pedal geometry?
who’s car are they driving? who’s car are they driving?
Controlling the stopControlling the stopBrake feel and vehicle control.Brake feel and vehicle control. The lower limit to gain is set by the weakest driver’s The lower limit to gain is set by the weakest driver’s
strength.strength. The upper limit to sensitivity or gain is set by The upper limit to sensitivity or gain is set by
controllability. controllability. Controllability = Driver perception of the relationship Controllability = Driver perception of the relationship
between their input and the braking system response.between their input and the braking system response.
Hair cells to judge decelerationHair cells to judge deceleration
Visual information (optic flow) used to judge TTC Visual information (optic flow) used to judge TTC and assess deceleration.and assess deceleration.
Assess current effort applied to pedal and adjust.Assess current effort applied to pedal and adjust.
Ability to adjust depends on system Ability to adjust depends on system gain/sensitivity.gain/sensitivity.
Should not be greater than driver’s threshold for Should not be greater than driver’s threshold for sensing differences in muscle effort.sensing differences in muscle effort.
Loss of lateral control is worse at higher gains:Loss of lateral control is worse at higher gains:
(Mortimer and Olsen, 1971)(Mortimer and Olsen, 1971)
Mean no of trials with loss of control
0
5
10
15
20
0.065 0.037 0.021 0.012 0.007 0.004
Deceleration/pedal force gain (g/lb.)
Pedals with travel resulted in fewer wheel lock-Pedals with travel resulted in fewer wheel lock-ups.ups.
Vehicle control problems for emergency Vehicle control problems for emergency
brakingbraking- pedal becomes isometric so less feedback - pedal becomes isometric so less feedback
for driverfor driver- driver at limit of effort so muscle control - driver at limit of effort so muscle control
reduced.reduced.
Hence ABS Hence ABS
When it all goes wrongWhen it all goes wrong
Case study: unintended Case study: unintended acceleration accidents.acceleration accidents.
ScenarioScenario- -
- automatic vehicle- automatic vehicle- - slow speed manoeuvre- - slow speed manoeuvre- - driver applies brakes but vehicle moves - - driver applies brakes but vehicle moves
forwardforward - driver applies more braking effort and - driver applies more braking effort and
vehicle moves faster!vehicle moves faster!- vehicle only stops following collision- vehicle only stops following collision
Reason – pedal confusion!Reason – pedal confusion!
Why did driver press wrong Why did driver press wrong pedal?pedal?
Only two pedalsOnly two pedals
Body twistBody twist
Similar pedal designSimilar pedal design
Pedal bay layout Pedal bay layout
(e.g. wheel arch)(e.g. wheel arch)
Why did driver continue to Why did driver continue to press wrong pedalpress wrong pedal
Efference copyEfference copy
The brain ‘knows’ where the foot is The brain ‘knows’ where the foot is because it sent the movement because it sent the movement messagemessage
Need for strong feedback to correct Need for strong feedback to correct this assumptionthis assumption
Why they don’t try other Why they don’t try other actionsactions
Incidents can last long enough for Incidents can last long enough for the driver to take other actions…the driver to take other actions…
––Switch off engineSwitch off engine
––Put into neutralPut into neutral
––Apply handbrakeApply handbrake
The flight or fight The flight or fight responseresponse
Sudden startling stimulusSudden startling stimulus
High risk of dangerHigh risk of danger
Action availableAction available
Action required immediatelyAction required immediately
HYPERVIGILANCEHYPERVIGILANCE
The hypervigilant stateThe hypervigilant state
Focus of attention on one activityFocus of attention on one activity
Awareness of sensory feedback Awareness of sensory feedback
restrictedrestricted
Cannot divide attentionCannot divide attention
Information processing disruptedInformation processing disrupted
Hypervigilance and vehicle Hypervigilance and vehicle controlcontrol
Incoming powerful stimuli (noise, view Incoming powerful stimuli (noise, view ahead) override any pedal error feedback ahead) override any pedal error feedback from pedalfrom pedal
Driver attends to steering - no processing Driver attends to steering - no processing
capacity to ‘work out’ what has happenedcapacity to ‘work out’ what has happened
No processing capacity to select other No processing capacity to select other
actionsactions
Preventative measuresPreventative measures
pedal designpedal design interlocksinterlocks trainingtraining
Hungry yet?Hungry yet?
Thank you for listeningThank you for listening
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