Human factors of braking Dean Southall Ergonomist Dean Southall Ergonomist Dean Southall Consultancy Dean Southall Consultancy

Bringing the car to a halt Getting on the brake Getting on the brake Applying efforts Applying efforts Controlling the stop Controlling the stop When it all goes wrong When it all goes wrong

Moving the foot to the brake pedal mean brake perception-reaction times of 1.5s mean brake perception-reaction times of 1.5s but affected by: - 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)

Pedals with travel resulted in fewer wheel lock-ups. Pedals with travel resulted in fewer wheel lock-ups. Vehicle control problems for emergency braking 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 Hence ABS

When it all goes wrong Case study: unintended acceleration accidents. Case study: unintended acceleration accidents.

Scenario Scenario- - automatic vehicle - - slow speed manoeuvre - - driver applies brakes but vehicle moves forward - driver applies more braking effort and vehicle moves faster! - 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 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 Focus of attention on one activity Awareness of sensory feedback restricted Awareness of sensory feedback restricted Cannot divide attention Cannot divide attention Information processing disrupted Information processing disrupted

Hypervigilance and vehicle control Incoming powerful stimuli (noise, view ahead) override any pedal error feedback from pedal 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 Driver attends to steering - no processing capacity to ‘work out’ what has happened No processing capacity to select other actions No processing capacity to select other actions

Preventative measures pedal design pedal design interlocks interlocks training training

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