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