Collision Warning Design 1

Collision Warning DesignTo Mitigate Driver Distraction

(CHI 2004)

Andrew Muller &

Eugene Khokhlov

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University of Iowa

• John D. Lee Ph.D.

• Elizabeth Hayes Daimler Chrysler (Chewbacca)

• Joshua D. HoffmanGrad Student

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To The Point:

• The Problem: Too many distractions while driving a car

• The Need: Collision warning system

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Background Information

• In-vehicle Information Systems (IVIS) are now feasible because:• Technology Advances• Societal Trends

• IVIS Functionality• Response Types• Critical Factors for IVIS

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Alert Strategies

• Warning Strategies• Graded• Single Staged

• Sensor Modality Presentation• Haptic (touch)• Auditory

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Experiment Goals

• Experiment 1• Examine how driver response depends on

graded and single stage warnings• Examine how driver response depends on

modality (haptic vs. auditory) of the warning

• Experiment 2• Examine how these warning strategies and

modalities affect driver preference

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Experiment 1 Method

• A mixed between/within-subject experimental design

• 3, 15-minute driving scenarios• 21 braking events (7x3)=21• 3 levels of severity• Speech-based email system to

distract the driver

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Participants

• 40 individuals• 20 female, 20 male

• Ages of 25 and 55 (licensed)• Unaware of the nature of the

research• Paid $20 each

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Apparatus

• Fixed-based, medium-fidelity driving simulator• 1992 Mercury Sable• 50-degree visual field of view• 640x480 screen• Visual collision warning icon• Needed elements for auditory and

haptic alerts

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DriveSafety (Hyperion)

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Experimental Design and Independent Variables

• Mixed between-within subject design

• Between subject variables• Warning modality• Warning strategy

• Within subject variables• Severity of lead vehicle breaking• If response was require

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Dependent Variables

• Safety benefit• Number of collisions• Adjusted minimum time to collision

(AMTTC)

• Driver response process (response followed by assessment or assessment followed by response)

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Procedure

• Operation instruction• Introductory drive (5 min)• 3 main drives (15 min/each)

• 7 braking events per drive @ 55mph• 1/7 was severe, always at end• Complete auditory email task

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Results

• 741 data points total• Repeated-measures ANOVA was

used to analyze the data using two-tailed hypothesis tests

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Results – Severity of braking events and driver response

• Drivers responded to braking events in a systematic and realistic manner• AMTTC reflected braking severity• Severity of lead vehicle braking affected

drivers’ braking response• Severity of braking affected mean

deceleration

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Results – Interface characteristics and safety benefit (collisions)• 40 potential collisions• 10 collisions occurred

• 7 in single-stage and 3 in graded• X2(1)= 2.13, p=0.144

• 5 in auditory and 5 in haptic

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Results – Interface characteristics and safety benefit (AMTTC)• Slight benefit for graded compared

to single-stage• F(1,36)=8.74, p=0.0055• Graded substantially better in severe

braking events

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AMTTC

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Response to nuisance alarm braking events

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Experiment 2 Method

• A within-subject experimental design

• 4, 10-minute scenarios• 24 braking events• 3 levels of severity• 2/3 of events required no driver

response

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Participants

• 20 individuals• 11 females, 9 males (licensed)• Between the ages of 25 and 55

• Unaware of the nature of the research

• Paid $20 each

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Apparatus & Independent variables and experimental design

• Same as in experiment 1

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Dependent variables

• Driver attitudes were measured with a series of subjective rating scales after each drive

• After completion of all trials, they comparatively ranked the systems

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Procedure

• Operation instruction• Introductory drive (5 min)• 4 main drives (10 min/each)

• 6 braking events per drive• Each scenario had an equal number

of event severity

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Results

• Rank the warning modalities in order from 1 to 4 based on preference• Violation of assumption of a repeated

measures ANOVA• Applied Friedman’s non-parametric analysis• Only when Friedman’s showed a significant

difference between conditions was a post-hoc multiple comparison performed using Fisher’s least significant difference method

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Conclusions

• Graded warning provided a greater safety margin

• Graded warning induced fewer inappropriate responses to the nuisance alarms

• Graded warning was more trusted• Warning modality had little effect on

performance in severe braking events• Haptic warnings were preferred on several

dimensions to auditory

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Questions

• In table 2, graded haptic beats single-stage haptic in everything except overall preference, what can account for this?

• Does the data on table 2 match what you would have expected?

• Graded is preferred for a one hour experiment, how about 5-10 years on daily basis?

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Questions

• Haptic is preferred over auditory in this study, is this a property of auditory or a property of the time span of the test, or some other factor?

• Why express haptic through a seat and not a gas pedal as in previous studies?