Johan Engström, Volvo Technology

Transportforum, Linköping 2011-01-13

Hur leder kritiska händelser till allvarliga olyckor?

Accidents and incidents

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Normal driving

Crash-Relevant EventCategory

Incid

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ype

Crash

Type

Severity

Type

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Crash-Relevant EventCategory

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Type

Severity

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p

Intro

• Key questions:– How do normal driving develop into critical events?– How do critical events develop into crashes?

• Traditionally: Limited data to answer these questions (crash reconstruction, subjective reports)

• Today– Naturalistic data with real crashes and near-crashes

captured on video– Need to know what to look for – need for an

accident model for micro-level analysis of the pre-crash phase

Anticipatory selection in driving

• Driving involves proactive selection of relevant information and actions

• Based on expectations on how an upcoming situation will develop

• Can be conceptualised in terms of schemata

Schemata

• Functional representations of actions, or action sequences making up a task

• Embody ”implicit” expectations

• Learned with experience

• Overlearned schemata often selected and excecuted automatically without conscious awareness, even at task level (”zombie behaviour”)

• Schema selection = attention selection

Turn right at intersection

Look left for carsSlow down Turn right

Task context schema

Basicschemata

Attention/action selection model

Schemata

Environment

Sensing Actuation

SchemataBasic

Task context

Cognitive control

SchemataTask context

Top-down

Bottom-up

• Task context and basic schemata

• Related schemata may compete for activation

• Schemata selected top-down (proactively) and/or bottom-up (reactively)

• Two types of top-down selection

– Context-driven (automatic, unconscious, inflexible)

– Cognitive control (effortful, conscious

Critical situations

Critical situations occur due to a conflict between the proactively selected schema and how the actual situation develops

Schemata

Environment

Sensing Actuation

SchemataLook for pedestrians

Task context

Cognitive control

SchemataDrive through intersection

Top-down

• Possible reasons:– Infrequent event

– Misleading traffic/infrastructure configuration

– Attentional ”capture” of competing schema (distraction)

– Unfamiliarity

– Working memory load

– ….

How do critical situations lead to crashes?

• Possible reasons:– Insufficient time to react– Stimulus outside field of view

(e.g. due to off-road glance)– Blink– Occlusion– Change blindness– Glare– Low stimulus saliency– Microsleep– ….

A critical situation will lead to a crash if last-second, reactive schema selection fails

Schemata

Environment

Sensing Actuation

SchemataBrake!

Task context

Cognitive control

SchemataDrive through intersection

Top-down

A general accident model

Normal driving

Critical event

Crash

Schema

Situation

Conflict ?Successful bottom-up selection?

No

Nearcrash

time

Reactive barrierProactive barrier

Yes

No

Yes

Real world example 1: Car-bicycle crashes at intersections and roundabouts (Summala and Räsänen, 2000)

Interpretation – Summala study

Driver’s schema: Look for cars to the left

Bottom-up selection: None since the bicyclist appears outside the field of view

Actual situationBicyclist approaching from the right

Normal driving

Critical event

CrashConflict ? No

Reactive barrierProactive barrier

Yes

Real-world example 2: Rear-end crash in the 100-car study

Narrative (by VTTI analyst): Subject driver is approaching a right turn at an intersection. The lead vehicle briefly stops at stop sign, then moves forward as if completing the turn. As the subject driver looks out his left window to check traffic, the lead vehicle stops again. The subject vehicle hits the lead vehicle in the rear. Inopportune glance.

Event 8633

Brake

GazeSpeed

Impact

Acceleration

Interpretation – 100 car rear end crash (event 8633)

Driver’s schema: Lead vehicle will continue to turn -> OK to look left to check traffic

Actual situationLead vehicle stops again

Bottom-up selection: None since the lead vehicle braking occurs outside the field of view

Normal driving

Critical event

CrashConflict ? No

Reactive barrierProactive barrier

Yes

Aggregate analysis, 8 rear-and crashes

Homogenousmechanisms!

Aggregate analysis, 8 near crashes

More heterogenousmechanisms!

Lee et al. (2007) quantitative analysis of 100-car study rear end events (same data)

Eyes-off-road is what distinguishes the crashes

TTC similar between crashes and near crashes

Some implications

• Hard to define ”crash-relevant events” in pure kinematic terms

• Data on driver’s proactive schema selection ideally requires both video and subjective report

• However, proactive selection often unconscious -> drivers may not be able to report! (aneqdotal data from Hanowski)

Conclusions

• A critical situation occur due to a mismatch between the proactively selected schema and how the actual situation develops -> breaking proactive barrier

• A critical event will lead to a crash if last-second, reactive schema selection fails -> breaking reactive barrier

• Accident/incident analysis at micro level should find out key mechanisms behind breaking of proactive and reactive barriers

• Requires combination of naturalistic and laboratory (simulator) data

• Future goal: Coherent taxonomy and classification scheme