Functional abilities needed to drive safely

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Functional abilities needed to drive safely

• Wendy Macdonald
• Centre for Ergonomics and Human Factors
• LA TROBE UNIVERSITY, Australia

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Safe Driving

• to drive in a way that minimises crash risk -
  to the extent thats practicable
• What functional abilities are needed to drive
  so as to minimise crash risk?

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Contexts and Purposes

• Many contexts e.g.
• Following injury/illness, to determine effects of
  injury or illness
• Re-licensing routine for everyone? or all older
  drivers?
• Part of general health check routine for older
  people?
• Following a crash everyone, or just older
  people?
• Pre- and post-remediation, as part of
  rehabilitation
• Self-monitoring?
• In general
• to ensure adequacy for safe driving

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Some useful conceptual frameworks ...

• 1. The road traffic system effects of vehicle,
  road traffic and environmental factors
• 2. Models of driving
• Required abilities vary with the driving
  environment
• Driving abilities are hierarchically organised
• Driving requires information processing and
  attentional resources

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Road traffic system- factors affecting required
abilities
In a socio-legal environment e.g. heavy
enforcement of drink-driving laws common
assumption that all adults have a driver license
intolerance of very slow drivers
In a physical road environment e.g. dark night
with poor lighting OR sunny day OR on a wet
slippery road, OR an unpaved rural road
In a traffic situation e.g. at a complex
signalised intersection, OR changing
driving in a lanes in narrow
lane heavy traffic,
beside a OR large
truck
Drive a vehicle Observe
Steer Control speed
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Driving as a hierarchical activity(Summala,
Michon)

• Strategic level
• Pre-driving personal values decisions re how
• much to drive trip purposes balancing goals
• When driving general strategies re route
  choices, time urgency, safety margins and lane
  choices
• Tactical level performing specific traffic
  maneuvers
• to adapt to demands of situation deciding to
• change lanes, overtake, slow down, etc.
• Operational level vehicle control actions
• perceiving environment and controlling the
  vehicle.

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Driving as a hierarchical activity(Hatakka et al)
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Driving as information processing demanding
attention resources
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A framework of functional abilities and
underlying capacities

• Functional abilities specific to driving
• Plus driving-specific values, attitudes, habits
• More general, underlying capacities
• Plus personality, general attitudes and habits

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Functional abilities specific to driving, and
some underlying abilities
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Driving-specific functional abilities
Sensory/Perceptual

• Maintain efficient visual searching/ scanning of
  the environment including use of mirrors,
  shoulder checks
• Read traffic situations especially
• Hazard Perception - notice specific hazards in
  good time to respond
• Monitor multiple events, dividing attention
  appropriately

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GENERAL CapacitiesSensory Perceptual

• Adequate vision (acuity tests static, dynamic,
  low contrast visual field), and other senses
• Flexibility of head, neck and upper torso (e.g.
  Head-Neck Rotation Test - MaryPODS, GRIMPS)
• Visual scanning / search skills (Trail Making B -
  MaryPODS, GRIMPS AutoTrails - CALTEST Useful
  Field of View Test)
• Ability to recognise partly occluded objects
  (Motor-free visual perception test visual
  closure sub-test MaryPODS, GRIMPS)
• Ability to predict trajectories of moving objects
  within 3-dimensional space

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Driving-specific functional abilities Vehicle
Control

• Maintain safety margins by appropriate
• speed for conditions
• lateral position within lane or carriageway
• position in relation to stationary
  objects/vehicles
• Control vehicle smoothly and accurately,
  including low-speed manoeuvring
• Use turn indicators and horn as required

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General Capacities Physical Psychomotor

• Lower limb strength and mobility (e.g. GRIMPS
  Rapid-Pace Walk Test Foot-Tapping Test)
• Motor response speed (e.g. DriveABLE, CALTEST
  AutoTrails)
• General physical strength endurance sufficient
  to operate the vehicle excessive fatigue
• Psychomotor coordination tracking and motor
  skills

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Driving-specific functional abilitiesCognitive

• Accurate mental models expectancies concerning
  roads and other road users enable prediction of
  what will happen next
• Maintain Situation Awareness
• Understand road laws road signs, etc
• Make judgments fast enough to cope with complex,
  fast-moving traffic

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General Capacities Cognitive

• Information processing capacity and processing
  rate (UFOV subtest 2 reaction times, total
  performance times)
• Working memory (Delayed Recall Test - MaryPODS
• Attentional resources and executive control
• divide attention between concurrent task
  components (UFOV Test subtest 2 - MaryPODS
  AutoTrails, UFOV - CALTEST attention shifting
  - DriveABLE Trail Making - MaryPODS, GRIMPS)
• maintain concentration and attentional focus,
  resisting distractions

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Which abilities are most important for safe
driving ?

• This is not obvious
• People with quite major physical impairments do
  not usually have a higher accident risk
• Driving errors that would lose points in a
  driving test may not be good indicators of risk.
• For example, some driving errors ...
• might be the type of error that is
  characteristic of experienced drivers and not
  indicative of declining competence
  Dobbs et al.(1998, p.369)

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The BEST evidence of unsafe driving is direct
observation of it

• Hazardous driving errors during a test
• crashes or near misses - driver at fault
• hazardous errors - crash avoided by chance, or
  actions of others - require supervisor
  intervention
• Global assessments of performance?
• - often poor inter-rater reliability
• Crash history (pre- or post-test) ?
• - high face validity, but poor reliability
  (quantity quality of exposure chance)

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Other evidence of unsafe driving

• Some driving-specific functional abilities
• Most driving errors are not immediately
  hazardous, but some of these are predictive of
  unsafe driving
• NB For each driving-specific ability, there are
  multiple underlying general abilities, but causal
  links between general abilities and driving
  behaviors are often unclear.
• Some general abilities
• Various tests but validity for SAFE driving ?

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Results from licensing authorityroad test
reports (n533)(Di Stefano Macdonald, 2003)

• Licence Review Test, Victoria, Australia
• Drivers referred because of queries re their
  competence (63 by police)
• Average age 76 years nearly half were 80 years

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Information recorded by tester

• Pass/Fail determined by testers overall global
  judgment
• Tester also records specific errors for each of 6
  performance categories
• Intersection negotiation
• Lane changing/diverging
• Position (in lane), and Speed
• Low speed manoeuvre
• Safety margin (headways, parked cars, etc)
• Car control

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e.g. possible errors for intersection
negotiation

• Mirror use
• Signaling
• Approach speed
• Obedience to signs/signals
• Judgment (re giving way to others)
• Turning

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Pass/Fail was determined by Tester Interventions
- i.e. hazardous errors
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Fail rates by age

• Overall Fail rate 46
• 
  Percent Failing

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Researcher-created performance score -
correlations with pass/fail, and with age
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Performance scores

• Error Category Performance
• Intersections 59
• Lane changing 35
• Position on road 60
• Low speed manvrs 55
• Safety margin 89
• Car control 86

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From these scores Predictors of pass/fail

• Logistic regression
• 6 performance scores together predicted 93.9 of
  pass/fail outcomes
• Addition of age did not significantly improve
  prediction

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Errors discriminating competent / non- competent
drivers (Dobbs et al, 1998)

• hazardous errors (supervisor intervention, or
  traffic adjusts)
• scanning (shoulder checks)
• positioning errors
• overcautious (speed gap acceptance)
• These errors consistent with crash data
• Non-competent based on on-road test, and
  discrimination of impaired / control drivers.

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So if safe driving is our focus

• Current evidence is that key functional
  (dis)abilities are these kinds of driving errors,
  since they are predictive of hazardous errors
  (which are directly unsafe).
• But what about higher order abilities and
  other driver characteristics ?

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Functional abilities specific to driving, and
some underlying abilities
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Driving as a hierarchical activity(Summala,
Michon)

• Strategic level
• Pre-driving personal values decisions re how
• much to drive trip purposes balancing goals
• When driving general strategies re route
  choices, time urgency, etc
• Tactical level performing specific traffic
  maneuvers
• to adapt to demands of situation lane choices,
  overtaking, etc.
• Operational level vehicle control actions
• perceiving environment and controlling the
  vehicle.

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If main focus is on crash risk

• Should we ALSO formally assess tactics and
  strategies ?
• Insight re ability understand own limitations ?
• Likelihood that will make strategic trip choices
  to reduce risk (knowledge, attitudes) ?
• Likelihood that will optimise driving tactics to
  reduce risk (knowledge, skills, attentional
  resources) ?
• At least, these should be key content in
  education training for older drivers