A Test Track Protocol for Assessing Forward Collision ... HS 811 501 July 2011 A Test Track Protocol for Assessing Forward Collision Warning Driver-Vehicle Interface Effectiveness

DOT HS 811 501 July 2011

A Test Track Protocol for Assessing Forward Collision Warning Driver-Vehicle Interface Effectiveness

DISCLAIMER

This publication is distributed by the U.S. Department of Transportation, National Highway Traffic Safety Administration, in the interest of information exchange. The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Department of Transportation or the National Highway Traffic Safety Administration. The United States Government assumes no liability for its contents or use thereof. If trade names, manufacturers names, or specific products are mentioned, it is because they are considered essential to the object of the publication and should not be construed as an endorsement. The United States Government does not endorse products or manufacturers.

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TECHNICAL REPORT DOCUMENTATION PAGE 1.ReportNo.

DOT HS 811 501 2.GovernmentAccessionNo. 3.Recipient'sCatalogNo.

4.TitleandSubtitleA Test Track Protocol for Assessing Forward Collision Warning Driver-Vehicle Interface Effectiveness

5.ReportDateJuly 2011

6.PerformingOrganizationCode

NHTSA/NVS-3127.Author(s)

Garrick Forkenbrock; NHTSA Andrew Snyder, Mark Heitz, Richard L. (Dick) Hoover, Bryan OHarra, Scott Vasko, and Larry Smith; Transportation Research Center, Inc.

8.PerformingOrganizationReportNo.

9.PerformingOrganizationNameandAddressNational Highway Traffic Safety Administration Vehicle Research and Test Center 10820 SR 347; P.O. Box B37 East Liberty, OH 43319-0337

10.WorkUnitNo.(TRAIS)

11.ContractorGrantNo.

12.SponsoringAgencyNameandAddressNational Highway Traffic Safety Administration 1200 New Jersey Avenue SE. Washington, DC 20590

13.TypeofReportandPeriodCovered

Final Report 14.SponsoringAgencyCode

NHTSA/NVS-312 15.SupplementaryNotesThe authors acknowledge the support of Lisa Daniels, Don Thompson, Thomas Gerlach Jr., Randy Landes, John Martin, Tim Van Buskirk, Matt Hostetler, Josh Orahood, Patrick Biondillo, and Ralph Fout, for assistance with vehicle preparation, instrumentation installation, test conduct, and data processing; and Scott Baldwin and Tom Ranney for insights into experimental design.

16. Abstract The primary objective of the work described in this report was to develop a protocol suitable for evaluating forward collision warning (FCW) driver-vehicle interface (DVI) effectiveness. Specifically, this protocol was developed to examine how distracted drivers respond to FCW alerts in a crash imminent scenario. To validate the protocol, a diverse sample of 64 drivers was recruited from central Ohio for participation in a small-scale, test track based human factors study. Each participant was asked to follow a moving lead vehicle (MLV) within the confines of a controlled test course and, while attempting to maintain a constant headway, instructed to perform a series of four distraction tasks intended to briefly divert their attention away from a forward-viewing position. With the participant fully distracted during the final task, the MLV was abruptly steered out of the travel lane, revealing a stationary lead vehicle (SLV) in the participants immediate path (a realistic-looking full-size balloon car). At a nominal time-to-collision (TTC) of 2.1s from the stationary vehicle, one of eight FCW alerts was presented to the distracted participant. Each alert modality was intended to emulate one or more elements from those presently available in contemporary vehicles. The timing of the critical events contained within the protocol appears to be repeatable, appropriate, and effective. With respect to evaluation metrics, the data produced during this study indicate that reaction time and crash outcome provide good measures of FCW alert effectiveness, where reaction time is best defined as the onset of FCW to the instant the drivers forward-facing view is reestablished. Using these criteria, the seat belt pretensioner-based FCW alerts used in this study elicited the most effective crash avoidance performance. That said, of the 32 trials performed with some form of seat belt pretensioner-based FCW alert, 53.1 percent of them still resulted in a crash. FCW modality had a significant effect on the participant reaction time from the onset of an FCW alert, and on the speed reductions resulting from the participants avoidance maneuvers (regardless of whether a collision ultimately occurred). Differences in participant response times from the instant their forward-facing view was reestablished to throttle release, brake application, and avoidance steer were not significant, nor were brake application and avoidance steer magnitudes. 17.KeyWords

Crash Warning Interface Metrics (CWIM), Forward Collision Warning (FCW), Driver Vehicle Interface (DVI), Test Track Evaluation

18.DistributionStatementDocument is available to the public from the National Technical Information Service www.ntis.gov

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Unclassified 20.SecurityClassif.(ofthispage)

Unclassified 21.No.ofPages

143 22.Price

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TABLEOFCONTENTSCONVERSIONFACTORS..................................................................................................................................................iiNOTEREGARDINGCOMPLIANCEWITHAMERICANSWITHDISABILITIESACTSECTION508........................................iiiLISTOFFIGURES.........................................................................................................................................................viiiLISTOFTABLES..............................................................................................................................................................xEXECUTIVESUMMARY................................................................................................................................................xiii1.0 BACKGROUND......................................................................................................................................................1

1.1 TheRearEndCrashProblem...............................................................................................................11.2 ForwardCollisionWarning(FCW)........................................................................................................11.3 TheCrashWarningInterfaceMetrics(CWIM)Program......................................................................1

1.3.1 CWIMPhaseIResearchPerformedatVRTCStaticTests.................................................21.3.1.1 PhaseIExperimentalDesign............................................................................21.3.1.2 UtilityofthePhaseIResults............................................................................6

1.3.2 CWIMPhaseIIResearchPerformedatVRTCProtocolRefinement................................61.3.2.1 PhaseIIExperimentalDesign...........................................................................61.3.2.2 PhaseIIDistractionTaskInterface...................................................................7

1.3.3 CWIMPhaseIIIResearchPerformedatVRTCFinalProtocol...........................................82.0 OBJECTIVES...........................................................................................................................................................9

2.1 ProtocolOverview...............................................................................................................................92.2 EvaluationConsiderations...................................................................................................................9

3.0 TESTAPPARTATUSANDINSTRUMENTATION.....................................................................................................103.1 TestVehicles......................................................................................................................................10

3.1.1 SubjectVehicle(SV)..........................................................................................................103.1.2 MovingLeadVehicle(MLV)..............................................................................................103.1.3 StationaryLeadVehicle(SLV)...........................................................................................11

3.2 ForwardCollisionWarning(FCW)Modalities....................................................................................123.3 TaskDisplays......................................................................................................................................13

3.3.1 HeadwayMaintenanceMonitor.......................................................................................133.3.2 RandomNumberRecallDisplay........................................................................................13

3.4 Instrumentation.................................................................................................................................143.4.1 SubjectVehicleInstrumentation......................................................................................143.4.2 MovingLeadVehicleInstrumentation..............................................................................153.4.3 PresentationofAuditoryCommandsandAlerts..............................................................153.4.4 VideoDataAcquisition.....................................................................................................15

4.0 TESTPROTOCOL..................................................................................................................................................164.1 Overview............................................................................................................................................164.2 ParticipantRecruitment.....................................................................................................................174.3 PrebriefingandInformedConsentMeeting.....................................................................................174.4 VehicleandTestEquipmentFamiliarization......................................................................................17

4.4.1 MaintainingaConstantHeadway.....................................................................................174.4.2 RandomNumberRecall....................................................................................................18

4.5 StudyCompensation..........................................................................................................................18

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TABLEOFCONTENTS(continued)

4.5.1 BasePay............................................................................................................................184.5.2 IncentivePay.....................................................................................................................18

4.6 PretestForwardCollisionWarningEducationandFamiliarization..................................................194.7 FCWAlertModalities.........................................................................................................................204.8 TestCourse........................................................................................................................................204.9 ExperimentalTestDrive.....................................................................................................................21

4.9.1 Pass#1of4.......................................................................................................................214.9.2 Pass#2of4.......................................................................................................................214.9.3 Pass#3of4.......................................................................................................................224.9.4 Pass#4of4.......................................................................................................................224.9.5 ParticipantDebriefingandPostDriveSurveyAdministration.........................................23

5.0 TaskParticipationandPerformance...................................................................................................................245.1 TestValidityRequirements................................................................................................................245.2 HeadwayMaintenance......................................................................................................................25

5.2.1 OverallHeadwayMaintenanceTaskPerformance...........................................................255.2.2 SubjectVehiclePerformanceDuringPass#4...................................................................265.2.3 MovingLeadVehiclePerformanceDuringPass#4..........................................................265.2.4 FCWAlertModalities........................................................................................................285.2.5 SubjectVehicleSpeedatFCWOnset................................................................................285.2.6 RangetoStationaryLeadVehicleatFCWOnset..............................................................305.2.7 SubjectVehicletoStationaryLeadVehicleTTCatFCWOnset........................................315.2.8 RandomNumberRecall....................................................................................................33

6.0 CrashAvoidanceResponseTimes.......................................................................................................................346.1 RandomNumberRecallTaskInstructionResponseTime.................................................................346.2 OverallVisualCommitmentDuration...............................................................................................366.3 VisualCommitmenttoOnsetofFCW................................................................................................376.4 OnsetofFCWtoEndofVisualCommitment.....................................................................................38

6.4.1 GeneralFCWtoVCendResponseTimeObservations......................................................396.4.2 StatisticalAssessmentofFCWtoVCendResponseTimes...............................................40

6.5 TimetoCollision(TTC)atEndofVisualCommitment......................................................................446.5.1 GeneralTTCatVCendObservations.................................................................................446.5.2 StatisticalAssessmentofTTCatVCend............................................................................45

6.6 ThrottleReleaseResponseTime........................................................................................................476.6.1 GeneralThrottleReleaseTimeObservations...................................................................48

6.6.1.1 OnsetofFCWtoThrottleReleaseTime.........................................................486.6.1.2 EndofVisualCommitmenttoThrottleReleaseTime....................................49

6.6.2 StatisticalAssessmentofThrottleReleaseTimes.............................................................506.6.2.1 ThrottleReleasefromFCWOnset..................................................................506.6.2.2 ThrottleReleasefromEndofVisualCommitment........................................53

6.7 BrakeApplicationResponseTime......................................................................................................556.7.1 GeneralBrakeApplicationResponseTimeObservations.................................................55

6.7.1.1 OnsetofFCWtoBrakeApplicationResponseTime.......................................556.7.1.2 EndofVisualCommitmenttoBrakeApplicationResponseTime..................57

6.7.2 StatisticalAssessmentofBrakeApplicationResponseTimes..........................................58

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6.7.2.1 BrakeApplicationTimefromFCWOnset.......................................................586.7.2.2 BrakeApplicationTimefromEndofVisualCommitment..............................61

6.8 AvoidanceSteerResponseTime........................................................................................................626.8.1 GeneralAvoidanceSteerResponseTimeObservations...................................................63

6.8.1.1 OnsetofFCWtoAvoidanceSteeringInput....................................................636.8.1.2 EndofVisualCommitmenttoAnAvoidanceSteeringInput.........................64

6.8.2 StatisticalAssessmentofAvoidanceSteerResponseTimes............................................666.8.2.1 OnsetofFCWtoAvoidanceSteerResponseTime.........................................666.8.2.2 EndofVisualCommitmenttoAvoidanceSteerResponseTime....................68

7.0 CrashAvoidanceInputMagnitudes....................................................................................................................717.1 PeakBrakePedalForce......................................................................................................................71

7.1.1 GeneralAssessmentofPeakBrakePedalForce...............................................................717.1.2 StatisticalAssessmentofPeakBrakePedalForce............................................................72

7.2 PeakSteeringWheelAngle................................................................................................................747.2.1 GeneralAssessmentofPeakSteeringWheelAngle.........................................................747.2.2 StatisticalAssessmentofPeakSteeringWheelAngle......................................................76

8.0 SubjectVehicleResponses..................................................................................................................................788.1 PeakLongitudinalDeceleration.........................................................................................................788.2 PeakLateralAcceleration..................................................................................................................78

9.0 CrashAvoidanceandMitigationSummary.........................................................................................................819.1 CrashAvoidance................................................................................................................................819.2 LikelihoodofanFCWAlertResponse................................................................................................819.3 SVSpeedReduction...........................................................................................................................86

9.3.1 GeneralSVSpeedReductionObservations......................................................................869.3.2 StatisticalAssessmentofFCWModalityonSVSpeedReductions...................................87

9.3.2.1 OverallSVSpeedReductions;CrashandAvoid.............................................879.3.2.2 SVImpactSpeedReductions(forTrialsResultinginaCrash)........................91

10.0 CONCLUSIONS.....................................................................................................................................................9510.1 TestProtocol......................................................................................................................................9510.2 EvaluationMetrics.............................................................................................................................9510.3 CrashAvoidanceManeuvers.............................................................................................................9610.4 ForwardCollisionWarningModalityAssessment.............................................................................97

11.0 FutureConsiderations.........................................................................................................................................9811.1 ProtocolRefinement(TimetoCollisionBasedTriggering)...............................................................9811.2 ProtocolValidation............................................................................................................................98

11.2.1 AlternativeStationaryLeadVehiclePresentationSchedule............................................9811.2.2 AlternativeCompensationSchedule................................................................................9911.2.3 EducationandTraining...................................................................................................100

11.3 ConsiderationofAdditionalFCWModalities...................................................................................10011.3.1 AlternativeSeatBeltPretensionerMagnitudesandTiming...........................................10011.3.2 LowMagnitudeBrakePulse...........................................................................................101

11.4 InteractionswithOtherAdvancedTechnologies.............................................................................10111.4.1 CrashImminentBraking.................................................................................................10111.4.2 DynamicBrakeSupport(DBS)........................................................................................101

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12.0 REFERENCES......................................................................................................................................................10313.0 APPENDICES......................................................................................................................................................104

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LISTOFFIGURES

Figure1. FCWVCenddurationasafunctionofalertresponselikelihoodandcrashoutcome...........................xvFigure1.1. VisualalertspresentedbytheVolvoS80,AcuraRL,andMercedesE350(fromlefttoright..................3Figure1.2. Randomnumberrecalldisplay(theredbuttonwasusedonlyduringPhaseIItrials)............................7Figure3.1. 2009AcuraRL,thesubjectvehicleusedinthisstudy...........................................................................10Figure3.2. 2008BuickLucerne,themovingleadvehicleusedinthisstudy...........................................................11Figure3.3. Inflatableballooncar,usedatthestationaryleadvehicleinthisstudy................................................11Figure3.4. Stationaryleadvehiclerestraintanchor................................................................................................12Figure3.5. VolvoS80FCWHUDhardwareinstalledinthesubjectvehicledashboard...........................................12Figure3.6. HeadwaymonitorinstalledintheSV.....................................................................................................13Figure3.7. Loadcellusedtomeasurebrakeforce.Noteadaptertoincreasethrottlestepheight.......................14Figure4.1. Leadvehiclecutoutscenario................................................................................................................16Figure4.2. Subjectvehicletostationaryleadvehicleimpact.................................................................................16Figure4.3. TRCSkidPaddimensionaloverview.......................................................................................................20Figure4.4. ChoreographyusedtoassessparticipantresponsestothevariousFCWmodalitiesusedinthis study.......................................................................................................................................................22Figure5.1. SVspeedatFCWalertonset,presentedasafunctionofFCWmodality...............................................29Figure5.2. SVspeedatFCWalertonset,presentedasafunctionofFCWmodalityandcrashoutcome...............30Figure5.3. SVtoSLVheadwayatFCWonset,presentedasafunctionofFCWmodality......................................30Figure5.4. SVtoSLVheadwayatFCWonset,presentedasafunctionofFCWmodalityandcrashoutcome.......31Figure5.5. SVtoSLVTTCatFCWonset,presentedasafunctionofFCWmodality...............................................31Figure5.6. SVtoSLVTTCatFCWonset,presentedasafunctionofFCWmodalityandcrashoutcome...............32Figure6.1. ResponsetimefromrecalltaskinstructiontoVCstart,presentedasafunctionofFCWmodality..........34Figure6.2. Visualcommitment(VC)sequence........................................................................................................35Figure6.3. ResponsetimefromrecalltaskinstructiontoVCstart,presentedasafunctionofFCWmodality andcrashoutcome.................................................................................................................................36Figure6.4. Overallvisualcommitmentduration,presentedasafunctionofFCWmodality..................................37Figure6.5. Overallvisualcommitmentduration,presentedasafunctionofFCWmodalityandcrashoutcome..37Figure6.6. VCstartFCWduration,presentedasafunctionofFCWmodality.........................................................38Figure6.7. VCstartFCWduration,presentedasafunctionofFCWmodalityandcrashoutcome.........................39Figure6.8. FCWVCendduration,presentedasafunctionofFCWmodality..........................................................39Figure6.9. FCWVCendduration,presentedasafunctionofFCWmodalityandcrashoutcome..........................40Figure6.10.TTCatVCend,presentedasafunctionofFCWmodality.........................................................................44Figure6.11.TTCatVCend,presentedasafunctionofFCWmodalityandcrashoutcome.........................................45Figure6.12.Throttlereleasetimes,presentedasafunctionofFCWmodality.........................................................48Figure6.13.Throttlereleasetimes,presentedasafunctionofFCWmodalityandcrashoutcome.........................49Figure6.14.Throttlereleasetimes,presentedfromVCendasfunctionofFCWmodalityandcrashoutcome..........49Figure6.15.Throttlereleasetimes,presentedfromVCendasfunctionofFCWmodalityandcrashoutcome..........50Figure6.16.Brakeapplicationtimes,presentedasafunctionofFCWmodality......................................................56Figure6.17.Brakeapplicationtimes,presentedasafunctionofFCWmodalityandcrashoutcome......................56Figure6.18.Brakeapplicationtimes,presentedfromVCendasfunctionofFCWmodality.......................................57Figure6.19.Brakeapplicationtimes,presentedfromVCendasfunctionofFCWmodalityandcrashoutcome.......58Figure6.20.Avoidancesteerresponsetimes,presentedasafunctionofFCWmodality.........................................63Figure6.21.Avoidancesteerresponsetimes,presentedasafunctionofFCWmodalityandcrashoutcome.........64

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LISTOFFIGURES(continued)Figure6.22.Avoidancesteerresponsetimes,presentedfromVCendasfunctionofFCWmodalityandcrash outcome.................................................................................................................................................65Figure6.23.Avoidancesteerresponsetimes,presentedfromVCendasfunctionofFCWmodalityandcrash outcome.................................................................................................................................................65Figure7.1. Peakbrakepedalforce,presentedasafunctionofFCWmodality.......................................................72Figure7.2. Peakbrakepedalforce,presentedasafunctionofFCWmodalityandcrashoutcome.......................72Figure7.3. Peaksteeringangle,presentedasafunctionofFCWmodality.............................................................75Figure7.4. Peaksteeringangle,presentedasafunctionofFCWmodalityandcrashoutcome.............................75Figure8.1. Peakdecelerationmagnitude,presentedasafunctionofFCWmodality.............................................78Figure8.2. Peakdecelerationmagnitude,presentedasafunctionofFCWmodalityandcrashoutcome.............79Figure8.3. Peaklateralaccelerationmagnitude,presentedasafunctionofFCWmodality..................................79Figure8.4. Peaklateralaccelerationmagnitude,presentedasafunctionofFCWmodalityandcrashoutcome..80Figure9.1. FCWVCenddurationasafunctionofalertresponselikelihoodandcrashoutcome...........................83Figure9.2. SpeedreductionfromonsetofFCWalert,presentedasafunctionofFCWmodality..........................86Figure9.3. SpeedreductionfromonsetofFCWalert,presentedasafunctionofFCWmodalityandcrash outcome.................................................................................................................................................87

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LISTOFTABLESTable1. FCWAlertModalitySummary...............................................................................................................xiiiTable2. FCWAlertResponseSummary...............................................................................................................xvTable1.1. CrashRankingsByFrequency(2004GESdata)........................................................................................1Table1.2. ExampleofContemporaryFCWModalities.............................................................................................3Table1.3. FCWAlertModalitiesInstalledIntoNHTSAAcuraRLforthePhaseIPilotTests.....................................4Table1.4. PhaseIBrakeReactionTimeSummary(n=728)......................................................................................5Table4.1. TaskPaymentSchedule..........................................................................................................................19Table4.2. FCWAlertModalitySummary................................................................................................................20Table5.1. HeadwayMaintenanceTaskPerformance............................................................................................25Table5.2. RepeatabilityofKeyParticipantandTestEquipmentInputsObservedDuringPass#4........................27Table5.3. RepeatabilityofKeyMovingLeadVehicleInputsDuringPass#4..........................................................28Table5.4. FCWAlertModalityConditionNumbers................................................................................................29Table5.5. SVtoSLVTTCAtFCWOnsetComparisonByModality.........................................................................32Table5.6. SVtoSLVTTCAtFCWOnsetComparisonByGender............................................................................32Table5.7. RandomNumberTaskRecallPerformanceSummary...........................................................................33Table6.1. FCWVCendComparisonByModality....................................................................................................41Table6.2. TestingtheEffectofHUDonFCWVCend.............................................................................................41Table6.3. FCWVCendComparisonByModality,Collapsed..................................................................................42Table6.4. FCWVCendPairWiseComparisons......................................................................................................42Table6.5. ObjectiveRankingFCWVCendofResponseTimes...............................................................................43Table6.6. FCWVCendResponseTimesByGender................................................................................................43Table6.7. FCWVCendResponseTimesandGenderInteraction...........................................................................43Table6.8. TTCatVCendComparisonByModality,Collapsed..................................................................................45Table6.9. TTCatVCendPairWiseComparisons......................................................................................................46Table6.10. ObjectiveRankingofTTCatVCend..........................................................................................................46Table6.11. TTCatVCendByGender..........................................................................................................................46Table6.12. TTCatVCendandGenderInteraction......................................................................................................47Table6.13. CrashAvoidanceResponseSummary(n=64).........................................................................................47Table6.14. ThrottleReleaseResponseTimefromFCWOnset................................................................................51Table6.15. TestingtheEffectofHUDonThrottleReleaseTimefromFCWOnset..................................................51Table6.16. ThrottleReleaseTimefromFCWOnsetComparisonByModality,Collapsed.......................................52Table6.17. ThrottleReleaseTimefromFCWOnsetPairWiseComparisons..........................................................52Table6.18. ObjectiveRankingofThrottleReleaseTimefromFCWOnset...............................................................52Table6.19. ThrottleReleaseTimefromFCWOnsetbyGender...............................................................................53Table6.20.ThrottleReleaseTimefromFCWOnsetandGenderInteraction..........................................................53Table6.21. ThrottleReleaseResponseTimefromVCend..........................................................................................54Table6.22. TestingtheEffectofHUDonThrottleReleaseTimefromVCend............................................................54Table6.23. ThrottleReleaseTimefromVCendComparisonByModality,Collapsed................................................54Table6.24. ThrottleReleaseTimefromVCendbyGender.........................................................................................55Table6.25. Brake/SteerResponseSummary(n=40)..............................................................................................55Table6.26. BrakeApplicationTimefromFCWOnset...............................................................................................58Table6.27. TestingtheEffectofHUDonBrakeApplicationTimefromFCWOnset................................................59Table6.28. BrakeApplicationTimefromFCWOnsetComparisonByModality,Collapsed.....................................59Table6.29. BrakeApplicationTimefromFCWOnsetPairWiseComparisons........................................................59

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LISTOFTABLES(continued)

Table6.30. ObjectiveRankingofBrakeApplicationTimefromFCWOnset.............................................................60Table6.31. BrakeApplicationTimefromFCWOnsetbyGender.............................................................................60Table6.32. BrakeApplicationTimefromFCWOnsetandGenderInteraction........................................................60Table6.33. BrakeApplicationTimefromVCend........................................................................................................61Table6.34. TestingtheEffectofHUDonBrakeApplicationTimefromVCend..........................................................61Table6.35. BrakeApplicationTimefromVCendComparisonByModality,Collapsed..............................................62Table6.36. BrakeApplicationTimefromVCendbyGender.......................................................................................62Table6.37. BrakeApplicationTimefromVCendandGenderInteraction..................................................................62Table6.38. DirectionofSteerSummary(n=42)........................................................................................................63Table6.39. AvoidanceSteerResponseTimefromFCWOnset................................................................................66Table6.40. TestingtheEffectofHUDonAvoidanceSteerResponseTimefromFCWOnset..................................66Table6.41. AvoidanceSteerResponseTimefromFCWOnsetComparisonByModality,Collapsed.......................67Table6.42. AvoidanceSteerResponseTimefromFCWOnsetPairWiseComparisons..........................................67Table6.43. ObjectiveRankingofAvoidanceSteerResponseTimefromFCWOnset..............................................68Table6.44. AvoidanceSteerResponseTimefromFCWOnsetbyGender...............................................................68Table6.45. AvoidanceSteerResponseTimefromFCWOnsetandGenderInteraction..........................................68Table6.46. AvoidanceSteerResponseTimefromVCend..........................................................................................69Table6.47. TestingtheEffectofHUDonAvoidanceSteerResponseTimefromVCend...........................................69Table6.48. AvoidanceSteerResponseTimefromVCendComparisonByModality,Collapsed................................69Table6.49. AvoidanceSteerResponseTimefromVCendbyGender........................................................................70Table7.1. PeakBrakePedalForceComparisonByModality..................................................................................73Table7.2. PeakBrakePedalForcePairWiseComparisons....................................................................................73Table7.3. PeakBrakePedalForceByModality,Collapsed....................................................................................73Table7.4. PeakBrakePedalForceByGender........................................................................................................74Table7.5. PeakSteeringWheelAngleComparisonByModality............................................................................76Table7.6. PeakSteeringWheelAnglePairWiseComparisons..............................................................................76Table7.7. PeakSteeringWheelAngleByModality,Collapsed..............................................................................77Table7.8. PeakSteeringWheelAngleByGender..................................................................................................77Table9.1. OverallCrashAvoidanceSummary........................................................................................................81Table9.2. SuccessfulSLVAvoidanceSummary......................................................................................................82Table9.3. SuccessfulSLVAvoidanceSummary,Collapsed.....................................................................................82Table9.4. FCWAlertResponseSummary...............................................................................................................83Table9.5. FCWAlertResponseSummary,Collapsed.............................................................................................84Table9.6. FCWResponseLikely,ButCrashNotAvoidedSummary.......................................................................85Table9.7. SVSpeedReductionComparisonByModality.......................................................................................88Table9.8. TestingtheEffectofHUDonSVSpeedReduction.................................................................................88Table9.9. SVSpeedReductionComparisonByModality,Collapsed.....................................................................88Table9.10. SVSpeedReductionPairWiseComparisons.........................................................................................89Table9.11. ObjectiveRankingofSVSpeedReductions............................................................................................89Table9.12. SVSpeedReductionbyGender..............................................................................................................89Table9.13. SVSpeedReductionandGenderInteraction.........................................................................................90Table9.14. SVSpeedReductionWithandWithoutSeatBeltPretensioning...........................................................90Table9.15. SVSpeedReductionWithandWithoutSeatBeltPretensioningandGenderInteraction....................90Table9.16. SVImpactSpeedReductionComparisonByModality...........................................................................91

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LISTOFTABLES(continued)

Table9.17. TestingtheEffectofHUDonSVImpactSpeedReduction.....................................................................91Table9.18. SVImpactSpeedReductionComparisonByModality,Collapsed.........................................................92Table9.19. SVImpactSpeedReductionPairWiseComparisons.............................................................................92Table9.20. ObjectiveRankingofSVImpactSpeedReductions................................................................................92Table9.21. SVImpactSpeedReductionbyGender.................................................................................................93Table9.22. SVImpactSpeedReductionandGenderInteraction.............................................................................93Table9.23. SVImpactSpeedReductionWithandWithoutSeatBeltPretensioning...............................................94Table9.24. SVImpactSpeedReductionWithandWithoutSeatBeltPretensioningandGenderInteraction........94TableA1. PhaseIStaticPilotPostTestQuestionnaireResponses......................................................................106TableC.1. RT3002ChannelsandAccuracySpecifications....................................................................................108

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EXECUTIVESUMMARYThe current phase of the National Highway Traffic Safety Administrations (NHTSA) CrashWarningInterfaceMetrics(CWIM)programisintendedtoidentifywhichalertmodalitiesmosteffectively assist distracted drivers in forward collision and lane departure crash scenarios.Once identified, theprogram seeks todevelop testprotocolsandevaluationmetrics tohelpassessthesafetybenefitsassociatedwiththesealerts.Ultimately,itisenvisionedthatNHTSAwillusetheoutputsoftheCWIMprogramtoencouragevehiclemanufacturersto implementFCW and Lane Departure Warning (LDW) alerts with a standardized interface design andoperationalcharacteristics.Theprimaryobjectiveoftheworkdescribed inthisreportwastodevelopaprotocolsuitablefor evaluating forward collision warning (FCW) drivervehicle interface (DVI) effectiveness.Specifically, thisprotocolwasdeveloped toexaminehowdistracteddrivers respond to FCWalertsinacrashimminentscenario.To validate theprotocol,adiverse sampleof64driverswas recruited from centralOhio forparticipationinasmallscale,testtrackbasedhumanfactorsstudy.Eachparticipantwasaskedtofollowamovingleadvehicle(MLV)withintheconfinesofacontrolledtestcourseand,whileattemptingtomaintainaconstantheadway,performaseriesoffourdistractiontasksintendedtobrieflydivert their attention away from a forwardviewingposition. With theparticipantfully distracted during the final task, theMLVwas abruptly steered out of the travel lane,revealingastationaryleadvehicle(SLV)intheparticipantsimmediatepath(arealisticlookingfullsizeballooncar). Atanominal timetocollision (TTC)of2.1s from theSLV,oneofeightFCWalertswaspresented to thedistractedparticipant. Eachalertmodalitywas intended toincorporateoneormore elements from thosepresently available in contemporary vehicles.Table1liststhealertmodalitiesusedinthisstudy,andthevehiclestheyoriginatedin.

Table1.FCWAlertModalitySummary.

FCWModality AlertOrigin

None Baseline(noalert)

VisualOnly 2008VolvoS80(HUD)

AuditoryOnly 2010MercedesE350(repeatedbeeps)

HapticSeatBelt 2009AcuraRL(reversibleseatbeltpretensioner)

Visual+Auditory 2008VolvoS80+2010MercedesE350

Visual+HapticSeatBelt 2008VolvoS80+2009AcuraRL

Auditory+HapticSeatBelt 2010MercedesE350+2009AcuraRL

Visual+Auditory+HapticSeatBelt 2008VolvoS80+2010MercedesE350+2009AcuraRL

The timing of the critical events contained within the protocol appears to be repeatable,appropriate, and effective. Presentation of task instructions and FCW alertswas accurately

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controlledand repeatable. Withvery fewexceptions,participantsmaintainedanacceptableheadway, began the random number recall taskwhen instructed to do so, andwere fullydistractedwhenpresentedwithanFCWalert.With respect toevaluationmetrics, thedataproducedduring this study indicate thatdriverreaction time and crashoutcomeprovide goodmeasuresof FCW alerteffectiveness. Manyvariantsofreactiontimewereexploredinthisstudy,howevertheintervaldefinedbytheonsetoftheFCWalerttotheendofvisualcommitment(i.e.,VCend,theinstantthedriverreturnstheirattention to a forwardfacing viewing position) appears to be themost appropriate.Whilereaction time from FCW to throttle release, brake application, and/or steering input alsoprovidegoodindicationsofFCWalerteffectiveness,itisimportanttoconsiderthatdriverscanusedifferenttechniquestoarriveatasuccessfulcrashavoidanceoutcome(e.g.,somedriversmayusesteeringbutnobraking).Interestingly,whileFCWmodalityhadasignificanteffectonthe participant reaction time, differences from the instant their forwardfacing view wasreestablished to throttle release,brakeapplication,andavoidancesteerwerenotsignificant,norwerebrakeapplicationandavoidancesteermagnitudes.Overall,17ofthe64participantsavoidedcollisionswiththeSLV(26.6percent).Fifteenofthesuccessfullyavoided crashes (88.2percent)occurredduring trialsperformedwith thehapticalert,oranalert combination inclusiveof thehapticmodality. One crash (1.6percent)wasavoidedduringatrialperformedwiththeauditoryonlyalert,onewithamodalitybasedonacombination of the auditory and visual alert. These results clearly indicate the seat beltpretensionerbasedhapticalertusedinthisstudyofferedbettercrashavoidanceeffectivenessthantheotherindividualmodalitiesonthetesttrack.However,theauthorsemphasizethatofthe32trialsperformedwithsomeformofthishapticalert,53.1percentofthemstillresultedinacrash.Whenconsideringthecrashvs.avoiddatapresentedinthisreport,itisimportanttorecognizethatbeing involved inacrashdoesnotnecessarily indicatetheparticipantdidnotrespondtotheFCWmodalityusedintheirindividualtrial.AlthoughmostparticipantscrashedintotheSLVbecause they failed to respond to the various FCW alerts used in this study (orwere notpresentedwithone),somecrashedbecausetheiravoidancestrategywassimplynoteffective.To quantify this phenomenon, the crash avoidance response of each participant wascategorizedinoneofthreeways:

1. FCWalertresponselikely,crashavoided

2. FCWalertresponselikely,crashnotavoided

3. FCWalertresponsenotlikely,crashnotavoidedAsummaryofcrashoutcome,presentedasa functionofFCWmodalityandcrashavoidanceresponse, is shown in Table2. Resultsof this categorizationwereused in conjunctionwithFCWVCenddurationasameansofquantifyingresponsetime,asshowninFigure1.Here,the

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rangeofresponsetimeswhereFCWalertresponseswerelikelyandthecrashavoidedwas270to870ms. ForthecaseswhereFCWalertresponseswere likelybutthecrashstilloccurred,responsetimeswerebetween330msto1.0second.Finally,fortheinstanceswhereFCWalertresponses were not likely, response times were between 870 ms to 1.74 seconds. If theparticipantdidnotrespondtotheFCWalert,acrashalwaysoccurred.

Table2.FCWAlertResponseSummary.

FCWAlertModality

#ofParticipants

ResponseLikely,CrashAvoided

ResponseLikely,CrashNotAvoided

ResponseNotLikely,CrashNotAvoided

None(noalert) 8

VisualOnly(VolvoHUD) 8

AuditoryOnly(MercedesBeep) 1 3 4

HapticSeatBeltOnly(AcuraBelt) 3 5

Auditory+Visual 1 2 5

Visual+HapticSeatBelt 5 1 2

Auditory+HapticSeatBelt 3 2 3

Visual+Auditory+HapticSeatBelt 31 3 1

Total(percentof63participants1)

161(25.4%)

11(17.5%)

36(57.1%)

1VCendvideodatanotavailableforoneofthe64participants.

Figure1.FCWVCenddurationasafunctionofalertresponselikelihoodandcrashoutcome.

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1.0 BACKGROUND1.1 TheRearEndCrashProblemUsing2004GeneralEstimatesSystem(GES)statistics,adatasummaryassembledbytheVolpeCenter1 indicated that approximately 6,170,000 policereported crashes of all vehicle types,involving 10,945,000 vehicles, occurred in the United States [1]. Many of these crashesinvolvedrearendcollisions,withthemostcommonprecrashscenariosbeingtheLeadVehicleStopped,LeadVehicleDecelerating,andLeadVehicleMovingatLowerConstantSpeed.Table1.1presentsasummaryofthe frequency,cost,andharm (expressedas functionalyears lost)for these crash types. For each parameter, the relevancewith respect to the overall crashproblemisprovidedinparentheses.

Table1.1.CrashRankingsByFrequency(2004GESdata).

PreCrashScenario Frequency Cost($) YearsLost

LeadVehicleStopped975,000(16.4%)

15,388,000,000(12.8%)

240,000(8.7%)

LeadVehicleDecelerating428,000(7.2%)

6,390,000,000(5.3%)

100,000(3.6%)

LeadVehicleMovingatLowerConstantSpeed210,000(3.5%)

3,910,000,000(3.3%)

78,000(2.8%)

1.2 ForwardCollisionWarning(FCW)NHTSAdefinesaforwardcollisionwarning(FCW)systemasoneintendedtopassivelyassistthedriver in avoiding or mitigating a rearend collision. These systems have forwardlookingvehicledetectioncapability,presentlyprovidedbysensingtechnologiessuchasRADAR,LIDAR(laser), cameras, etc. Using information from these sensors, an FCW system drivervehicleinterface, or DVI, alerts the driver that a collision with another vehicle in the anticipatedforward pathway of their vehicle may be imminent unless corrective action is taken.Contemporary FCW systems typically include various combinationsof audible, visual, and/orhapticwarningmodalities,presentedtogetherasasingleconcurrentalert.1.3 TheCrashWarningInterfaceMetrics(CWIM)ProgramThe current phase of the National Highway Traffic Safety Administrations (NHTSA) CrashWarningInterfaceMetrics(CWIM)programisintendedtoidentifywhichalertmodalitiesmosteffectively assist distracted drivers in forward collision and lane departure crash scenarios.1 The Volpe Center is part of the US Department of Transportations Research and Innovative TechnologyAdministration(RITA).

2

Once identified, theprogram seeks todevelop testprotocolsandevaluationmetrics tohelpassessthesafetybenefitsassociatedwiththesealerts.Ultimately,itisenvisionedthatNHTSAwillusetheoutputsoftheCWIMprogramtoencouragevehiclemanufacturersto implementFCW and Lane Departure Warning (LDW) alerts with a standardized interface design andoperationalcharacteristics.In support of the CWIM program, the University of Iowa is presently using the NationalAdvancedDrivingSimulator(NADS)todeveloptestprotocolsrelevanttotheforwardcollisionand lanedeparture safety concerns. Theworkdescribed in this reportwas theoutputof aconcurrentprogramperformedatNHTSAsVehicleResearchandTestCenter(VRTC),designedtoprovideobjectivetesttrackbaseddatarelevanttotheforwardcollisionproblem.Thisworkwascompletedinthreephases:PhaseI.AsmallsamplepopulationwasexposedtoalargenumberofFCWalertmodalitiesinasimpledetectionexerciseusingarepeatedmeasureexperimentaldesign. ResultsfromthesetestswereusedtoreducethenumberofFCWalertcombinationsusedinPhaseII.Phase II. A small sample of drivers recruited from the general public participated in anexperimentaldriveonthetesttrack.ObservationsmadeduringtheconductofthisphasewereusedtorefinethetestprotocolultimatelyusedinPhaseIII.Phase III. Sixtyfourdriversrecruitedfromthegeneralpublicparticipated inanexperimentaldriveonthetesttrack.SevenFCWalertmodalitycombinationsandabaselineconditionwereused in thisphase. Dataoutput from trialsperformedwitheachFCWalertwere comparedbetweentestparticipants.1.3.1 CWIMPhaseIResearchPerformedatVRTCStaticTestsTheCWIMworkperformedatVRTCbeganbyidentifyingwhatFCWalertmodalitiesexistedoncontemporary production vehicles. A description of the systems representative of thoseavailableonUSspecificationvehicles ispresented inTable1.2. Ofsignificance isthediversityof thealerts. At the time the testsdescribed in this reportwereperformed, thenumberofcontemporarylightvehiclesavailableintheUnitedStateswithFCWwasquitelow.

Since itwasnot feasible toperforma largescaleevaluation inclusiveofeach FCWmodalityshown inTable1.2,Phase Iresearchconsistedofasmallstaticstudydesigned toreduce thenumberofauditoryandvisualalertstooneapiece.1.3.1.1PhaseIExperimentalDesignPreparationforthePhaseIstaticstudybeganwithFCWalertsrepresentativeofeachmodalityshowninTable1.2beinginstalledintoacommonsubjectvehicle(SV),a2009AcuraRL2.While

2Thisretrofitonlyinvolvedinstallationofmultiplealerts,notoftheotherhardware,etc.usedtoactivatethem.

3

theauthorsaresensitive to the likelihoodvehiclemanufacturersdesign theirrespectiveFCWalerts tobe integratedsystemsappropriate for thevehicle inwhich theywere installed (e.g.,theauditoryalertwas selected tocomplement thevisualalert,etc.), installingmultiplealertmodalities intoonevehicle removed theconfoundingeffectofvehicle type fromsubsequentanalyses.

Table1.2.ExampleofContemporaryFCWModalities.

Alert

Vehicle

2009AcuraRL

2010ToyotaPrius

2010MercedesE350

2008VolvoS80

2010FordTaurus

2011AudiA8

HapticSeatBelt

Pretensioner

SeatBeltPretensioner

BrakePulse(0.25g)

VisualBrakeonthe

MDC1BrakeontheMDC1

SmallIC2Icon LEDHUD LEDHUDBrakeGuardActivatedontheMDC1

Auditory Beep Beep Beep Tone Tone SingleGong

1MDC=MessageDisplayCenter 2IC=InstrumentCluster

Three different visual alert implementations were examined. In addition to the SVsmanufacturerequippedmessage display center alert, an LED headup display (HUD) from a2008 Volvo S80 and a small FCW icon from a 2010Mercedes E350 were installed in thedashboardand instrumentcluster,respectively,toemulatethealertsnativeenvironmentstothegreatestextentpossible(seeFigure1.1).

Twononnativeauditoryalertswereused,originating froma2010MercedesE350 (repeatedbeeping ) and a 2008 Volvo S80 (repeated tone ). One haptic alertwas used, the SVsmanufacturerequipped seat belt pretensioner. Table 1.3 provides a summary of the alertsinstalledintheSV.Phase I tests were performed with eight participants recruited from within VRTC. UponenteringtheSV,participantswereinstructedtoadjusttheirseattoacomfortablepositionand

Figure1.1.VisualalertspresentedbytheVolvoS80,AcuraRL,andMercedesE350(fromlefttoright).

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drivetoatestcourseisolatedfromotherfacilitytraffic.Onceatthecourse,participantswereinstructedtostopthevehicle,putthetransmissioninpark,andfaceforwardwiththeirhandsat the3and9oclockpositionson thesteeringwheel. Verbal instructionswereprovided toeachparticipantbyaninvehicleexperimenterwhooccupiedtheleftrearseat.AllPhaseItestswereperformedduringdaylighthours.

Table1.3.FCWAlertModalitiesInstalledIntoNHTSAAcuraRLforthePhaseIPilotTests.

Visual Auditory Haptic

BrakeontheMDC

SmallIcon LEDHUD None Beep Tone NoneSeatBelt

PretensionerNone

*MDC=MessageDisplayCenter

Amonitor was attached to the base of thewindshield near the passengerside Apillar todisplay realtime throttleposition.Participantswere instructed towatch themonitor for thedurationofeachtesttrial inordertomaintainaconstantthrottleapplicationof3.5percent3.Bymonitoringthethrottleposition,theparticipantseyesweredirectedawayfromaforwardlookingviewingposition,howeverperipheralvisionstillallowedthemtodetectactivitytowardthefrontofthevehicle(i.e.,FCWalertstatus).ParticipantswereinformedthattheywouldbepresentedwithavarietyofdifferentFCWalerts,andtoldtoreleasethethrottleandapplyforcetothebrakepedalwhenthealertfirstbecameapparent.Followingacknowledgementofanalert,participantswereinstructedtoreleasethebrakepedal,andresumeaconstantthrottlepositionof3.5percent.Presentation of the FCW alerts used in Phase Iwas a repeatedmeasure. During their testsession,eachparticipantreceivedfourrandomizedsequencesof23alertcombinations(i.e.,allpossible combinationsof thealerts shown inTable1.3,except the noalert configuration).Therefore,eachsubjectreceivedatotalof92individualalertsduringPhaseI.Toquantifyalertdetectability, brake response time from the onset of FCW was measured for each trial.Followingcompletionofthefinaltrial,the invehicleexperimenterpresentedeachparticipantwithaseriesofquestionsaskingtheiropinionofthealerts,includingwhichauditoryandvisualalertwasthemostapparent4.Acompletelistofthequestionsandthesubsequentresponsesareprovided inAppendixA. Table1.4summarizes thebrakereactiontimesobservedduringthePhaseItrials.

3ItisanticipatedthattheoutsidetemperaturewillbeverywarmduringconductofthePhaseItests.Therefore,participant comfortwill require thevehiclesair conditioning (and thus theengine)andbeon. Instructing theparticipantstomaintainamoderatetolargethrottlepositionwiththevehicleatrestwouldresultinhighengineRPM;apotentiallydistractingsituationthatcouldconfoundtheabilityoftheparticipantstodetectand/orrespondtotheFCWalerts.4Subjects1and2werepresentedwithasmallersetofposttestquestions;onlyquestions1,7,and15wereused.

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Table1.4.PhaseIBrakeReactionTimeSummary(n=728).

DescriptionBrakeReactionTime(seconds) Missed

TrialsMin Max Mean StdDev

AcuraBelt,AcuraMDC 0.325 0.820 0.507 0.149

AcuraBelt,MercedesBeep,MercedesIC 0.330 0.865 0.516 0.155

AcuraBelt,VolvoTone 0.285 1.080 0.518 0.187

AcuraBelt,MercedesBeep,VolvoHUD 0.310 0.850 0.520 0.162

AcuraBelt,MercedesBeep,AcuraMDC 0.310 1.120 0.524 0.170

AcuraBelt 0.320 0.910 0.527 0.160

AcuraBelt,VolvoTone,AcuraMDC 0.290 0.905 0.529 0.163

AcuraBelt,VolvoHUD 0.315 1.025 0.532 0.176

AcuraBelt,MercedesIC 0.330 0.920 0.534 0.180

AcuraBelt,MercedesBeep 0.335 0.950 0.538 0.188

AcuraBelt,VolvoTone,MercedesIC 0.290 1.070 0.540 0.191

AcuraBelt,VolvoTone,VolvoHUD 0.320 0.990 0.557 0.200

MercedesBeep,MercedesIC 0.510 1.085 0.690 0.143

VolvoTone,VolvoHUD 0.465 1.035 0.705 0.156

VolvoTone,AcuraMDC 0.470 1.125 0.708 0.187

MercedesBeep,VolvoHUD 0.460 1.535 0.713 0.237

MercedesBeep,AcuraMDC 0.405 1.425 0.747 0.245

MercedesBeep 0.495 1.065 0.752 0.173

VolvoTone,MercedesIC 0.460 1.535 0.786 0.281

VolvoTone 0.475 1.365 0.797 0.200

MercedesIC 0.495 3.395 1.065 0.563 4of32

AcuraMDC 0.500 4.330 1.088 0.785 3of32

VolvoHUD 0.505 2.940 1.158 0.577 1of32

Note:HUD=headupdisplay,IC=instrumentcluster,MDC=messagedisplaycenterInTable1.4, results from testsperformedwithauditoryalertsonlyarehighlighted ingreen.Similarly, tests performedwith visual alerts only are highlighted in blue. Results from alertconfigurations containing seat belt pretensioning (i.e., those containing Acura Belt in thedescriptioncolumn)areshowninorange.Notethatatotalof728datapointsaresummarizedinTable1.4. Ofthe736testsperformed(8subjects*92testspersubject),eightresulted inmissedtrialsbecausetheparticipantsdidnotdetectthepresentationoftheFCWalert.Missedtrialsonlyoccurredduringoneofthethreevisualonlyconfigurations.

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1.3.1.2UtilityofthePhaseIResultsDependingon theanalysisperformed,differences inbrake reaction timeobserved inPhase Iwere either marginally significant or not statistically significant (an analysis is provided inAppendix B). Therefore, the participants subjective impressions of the two auditory alertswere used to determine which to include in subsequent test phases. When asked whichauditory alertwas themost noticeable, six of the eight responses indicated the MercedesBeep. Twoparticipants indicatedbothauditoryalertswereequallyapparent. Fiveofthesixparticipants indicated theMercedes beepbased alertwas obvious, attention getting, orurgent.Basedonthisfeedback,theMercedesBeepwasretainedforlateruseasthesoleauditoryalert.Thedecisiononwhichvisualalerttoincludeinsubsequenttestphaseswasconfoundedbythefact each visualonly configuration produced missed trials. Four of the eight participantsconsidered the Acuramessage display centerbased visual alert to be themost apparent,followedby theVolvoHUD (threeparticipants), then theMercedes instrumentclusterbasedalert (one participant). Given that the differences inmean brake reaction time were notsignificantlydifferentacrossvisualalerttype,andsincethenumberofmissedtrialswaslowestfor tests performedwith theVolvoHUD only (i.e.,when compared to the other visualonlyalerts),theVolvoHUDwasretainedforlateruse.1.3.2 CWIMPhaseIIResearchPerformedatVRTCProtocolRefinementOnce the reducedsetofFCWmodalitieshadbeen identified,work to refine theprotocol forevaluatingdrivervehicleinterface(DVI)effectivenesswasperformed.Unlikethestatictestingused in Phase I, Phase II testswere highly dynamic, placing participants recruited from thegeneralpublicinarealisticcrashimminentdrivingscenario.1.3.2.1PhaseIIExperimentalDesignAt a high level, the Phase II protocol asked participants to perform two tasks during anexperimental drive on a controlled test course. First, they were instructed tomaintain aconstant distance between their vehicle and another being driven directly in front of them.Second, while maintaining a constant headway, participants were asked to direct theirattentionaway fromtheroadtoobserveaseriesofthreerandomnumberspresentedonaninterfacelocatedneartherightfrontseatheadrest.Afterthelastnumberhadbeenpresented,participantsweretoldtoreturntoaforwardlookingviewingpositionandrepeatthenumbersaloudtoaninvehicleexperimenter(whooccupiedtheleftrearseatingposition).Late in theirdrive,duringaperiodofdistraction imposedby therandomnumberrecall task,the leadingvehicleperformedanabrupt lanechangethatsuddenlyrevealedastationary leadvehicle directly in the path of the participants vehicle. Shortly thereafter, distractedparticipantswerepresentedwithanFCWalertselectedfromthereducedsetofalertsoutput

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fromPhaseI.UnliketherepeatedmeasuresexperimentaldesignusedinPhaseI,eachPhaseIIparticipantonlyreceivedoneFCWalert.1.3.2.2PhaseIIDistractionTaskInterfaceOfparticularinterestforPhaseIIwasdevelopmentofawaytodirecttheparticipantsforwardfacing view away from the road for as long as possible, while retaining excellent taskacceptancewithalowlikelihoodofaforwardlookingglance.Arandomnumberrecalltaskwasdevelopedinanattempttosatisfythesecriteria.InPhaseII,therandomnumberrecalltaskwasbasedona4.5x3.5display, installedtotheleftoftheSVfrontpassengerheadrest,asshowninFigure1.2.Asinitiallyconceived,thetaskrequired aparticipant to (1)push a redbutton to the rightof thenumericaldisplay, (2)bepresentedwiththreerandomsingledigitnumbers, (3)releasethebutton,and (4)repeatthenumbersaloudtoan invehicleexperimenter (intheordertheywereshown). Observingthenumbers required the participant fully avert their forwardfacing view from the road. Eachnumberwaspresentedforapproximately750ms.

Figure1.2.Randomnumberrecalldisplay(theredbuttonwasusedonlyduringPhaseIItrials).Conceptually,thePhaseIIrandomnumberrecalltaskwasappealingbecauseitwasbelievedtoimposereasonablephysicalandmentalcommitmentsupontheparticipantswhilekeepingtheirforwardfacingviewawayfromtheroadforanextendedperiodoftime.PilottestsperformedwithsubjectsrecruitedfromwithinVRTCproducedencouragingresults;thetaskwasgenerallyconsideredtobechallenging,yetcomfortable.Unfortunately, tests performed with members from the general public revealed a majordeficiencyinthetaskdesign.Althoughthefirstparticipantfullyengagedthephysical(pushedthebutton)andcognitive (committedtherandomnumberstomemory)elementsofthetaskimmediatelyafterbeinginstructedtodoso,thenextsevendidnot.Instead,theseparticipantsdividedthetaskintotwoseparatecomponents.Wheninstructedtobegintherandomnumbertask, these participants reached for the task display and located the task activation button

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entirelybytouch.However,sincetheparticipantswereabletomaintaintheirforwardlookingviewingpositionwhileengaged inthisspatialdetection,theycouldobservethechoreographyintended to produce a surprise event near the end of their experimental drive (i.e., thesuddenlyrevealedstationaryleadvehicle).Sinceconcealingthischoreographywasanintegralpartofthetestprotocol,additionalrefinementwasrequired.1.3.3 CWIMPhaseIIIResearchPerformedatVRTCFinalProtocolUsinglessonslearnedfromPhasesIandII,theauthorsdevelopedthePhaseIIIFCWevaluationprotocol. This protocol offered an excellent combination of participant acceptance,performability,objectivity,anddiscriminatory capability. ThePhase IIIprotocolwasused toproducethedatadiscussedintheremainderofthisreport.Atotalof64subjectsparticipatedinthePhaseIII.

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2.0 OBJECTIVESTheobjectivesofthePhaseIIICWIMFCWworkperformedatVRTCwereto:

1. DeveloparobustprotocolforevaluatingFCWDVIeffectivenessonthetesttrack.

2. PerformasmallscalehumanfactorsstudytovalidatetheCWIMFCWprotocol.

3. EvaluatehowdifferentFCWalertmodalitiesaffectparticipantreactiontimesandcrashavoidancebehavior.

2.1 ProtocolOverviewTheprotocolusedinthisstudywasdevelopedtoexaminehowdistracteddriversrespondedtoFCWalertsinacrashimminentscenario.AdiversesampleofdriverswasrecruitedfromcentralOhio forparticipation in the study. Theseparticipants,usingagovernmentownedSV,wereinstructed to follow amoving lead vehicle (MLV) through a test trackbased course whilemaintainingaspecifiedspeedandheadway. Duringthedrive,participantswere instructedtocompleteadistractiontaskrequiringthemtolookawayfromtheroadforthedurationofthetask.To familiarize participantswith the vehicle, driving environment, and distraction task, theyperformedmultiplepassesthroughthetestcourse.Duringthefinalpass,withthedriverfullydistracted,theMLVunexpectedlyswervedoutofthe laneoftraveltorevealastationary leadvehicle (SLV) in theparticipantspath. In this study, theSLVwasactuallya fullsize realisticlookinginflatable.2.2 EvaluationConsiderationsThe data produced in this studywere reduced and analyzedwithmethods that objectivelydescribed how the participants responded to different FCWmodalities. Evaluationmetricsquantifieddifferencesinthetimingandmagnitudeofdriversavoidancemaneuvers.Fromaprotocolassessmentperspective, theauthorswere interested in confirming that theexperimental design andmethodology used in this study could effectively, objectively, andrepeatablyquantifytheparticipantswillingnesstoperformtheprotocolstasks,andtheabilityoftheprotocoltodiscriminatebetweenbaseline(i.e.,noalertpresented),apparent,andnonapparentalerts.From a driver performance perspective, the primary data of interest straddled the crashimminent scenario: (1) theTTCwhenparticipants returned to their forwardlookingviewingposition,(2)throttlerelease,brakeapplication,andavoidancesteerresponsetimesfromFCWalertonset,(3)themagnitudesoftheparticipantsbrakeandsteer inputs,(4)themagnitudesoftheSVspeedreductionsandaccelerations,andwhetherthetestparticipantscollidedwiththeSLV.

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3.0 TESTAPPARTATUSANDINSTRUMENTATION3.1 TestVehicles3.1.1 SubjectVehicle(SV)TheSVused inthisstudywasa2009AcuraRL,shown inFigure3.1. Originallyequipped,thisfourdoorsedanwasequippedwithallwheeldrive,fourwheelantilockdiscbrakeswithbrakeassist,electronic stability control (ESC),an FCW system,anda crash imminentbrake system(CIB).Duringconductof the testsperformed in thisstudy,an invehicleexperimenteroccupied theleftrearseatingposition. Toobservetestdataas itwasbeingcollected,tabulateparticipantperformance, and manually activate elements of the test protocol during pretestfamiliarization,an interfacewiththevehiclesdataacquisitionandaudiosystemwas installedbehindthedriverseat.

3.1.2 MovingLeadVehicle(MLV)Themoving leadvehicle (MLV)used in thisstudywasa2008BuickLucerne,shown inFigure3.2.Thismidsizedsedanwasselectedprimarilyoutofconvenience;itwasavailable,hadbeenpreviouslyinstrumentedwithmuchoftheequipmentrequiredbytheprotocoldescribedinthisreport,andwas largeenoughtoeffectivelyobscurethesubjectsviewoftheSLVpriortothesurpriseeventpresentedattheendoftheexperimentaldrive.OfnoteinFigure3.2isthesolidblack verticalpanel installedbehind the front seats. Thispanelpreventedparticipants fromlooking through theMLVduring theirdrive, thereby reducing the likelihoodof theSLVbeingprematurelydetectedonapproach. Forthisstudy,theMLVwasdrivenbyaprofessionaltestdriver.MLVspeedwasmaintainedusingcruisecontrolformuchoftheexperimentaldrive.

Figure3.1.2009AcuraRL,thesubjectvehicleusedinthisstudy.

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3.1.3 StationaryLeadVehicle(SLV)TheFCWalertsused inthisstudywerepresentedataTTCof2.1seconds;avaluebelievedtobe representativeof thoseusedbyalgorithms installed incontemporaryproductionvehicles.RespondingtoanalertpresentedatthisTTCwasintendedtoprovideparticipantswithenoughtimetosuccessfullyavoidtheSLV.However,sincethisstudyalsoincludedabaselineconditionwhere no alerts were presented, SVtoSLV collisions were to be expected. To insureparticipantsafety,afullsize inflatableballooncar,designedtoemulatea2009VolkswagenGTI(showninFigure3.3)wasused.

TheSLVwasapproximately5ftwide,5fttall,12ftlong,andweighed77lbs.Itwasstrikeable,inflatable inthe field,andsecuredtothegroundwithziptiesandconcreteanchors. Thezipties,presentateachcorneroftheSLV,werestrongenoughtopreventthevehiclefrommovinginresponsetowindgusts,buteasilysnappedduringaSVtoSLVcollision. TheSLVrestraintsareshowninFigure3.4.

Figure3.2.2008BuickLucerne,themovingleadvehicleusedinthisstudy.

Figure3.3.Inflatableballooncar,usedatthestationaryleadvehicleinthisstudy.

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Figure3.4.Stationaryleadvehiclerestraintanchor.3.2 ForwardCollisionWarning(FCW)ModalitiesAspreviouslyexplainedinSection1.3.1.2,thevisualFCWalertoriginallyinstalledintheSVwasdisabled in lieuofusing that froma2008VolvoS80. Specifically, theVolvoS80 visualalertconsistedofa6inch lightbar that,whenactivated, flasheda seriesof twelve lightemittingdiodes(LED)usinga50percentdutycyclefor4seconds(100mson,100msoff).Areflectionofthelightbarilluminationwasvisibletothedriverintheformofaheadupdisplay(HUD)onthewindshield, intendedtoreside in lineofsightforeasydetection. Figure3.5showswherethehardwareVolvoFCWHUDhardwarewasinstalledinthedashoftheSV.Alsoasexplained inSection1.3.1.2, theauditoryFCWalertoriginally installed in theSVwasdisabled in lieuofusingthatfroma2010MercedesE350. Specifically,thisauditoryalertwascomprisedoftensharpbeepsusingtheaudioclipprovided inSection1.3.1.1. Althoughverysimilar to that installed in the SV, use of theMercedesbased alert allowed the authors todiversifytheoriginsoftheFCWalertsusedinthisstudy.

Figure3.5.VolvoS80FCWHUDhardwareinstalledinthesubjectvehicledashboard.

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Themagnitude of the seat belt pretensioner activation used in this studywas intended tocloselyemulatethatoftheoriginal2009AcuraRLbasedconfiguration.However,thetimingofwhenthe interventionoccurredwasadjustedtobe inagreementwiththeauditoryandvisualalerts(i.e.,thecommandedonsetofeachalertwasequivalent).Note:AlthoughtheSVwasequippedwithaforwardlookingradartoproviderangeandrangeratedatatothevehiclesFCWcontroller,theauthorsoptedtoactivateeachFCWalertusinganexternal control computer and positionedbased trigger points. This provided excellentactivationrepeatability,andavoidedthepotentialfortheoriginalsensingsystembeingunabletoacquireandrespondtotheSLVinthelimitedtimeavailableprecrash.3.3 TaskDisplays3.3.1 HeadwayMaintenanceMonitorToassisttheparticipantswithachievingandmaintainingtheappropriatedistancetotheMLVduringeachpass,a3.25x2.0monitordisplayingtherealtimeheadwaywasattachedtothebaseofthewindshield,justabovetheSVdashboard(seeFigure3.6).

3.3.2 RandomNumberRecallDisplayDuringeachpass,andwhilemaintainingthedesiredheadway,participantswere instructedtocompleteatotalof fourrandomnumberrecalltasks. Duringtheconductofthesetasks, fiverandomlygeneratedsingledigitnumberswerepresentedona4.5x3.5display installedtothe leftof theSV frontpassengerheadrest (previouslyshown inFigure1.2). The increase tofivenumbers,fromthethreeusedduringthepreliminaryPhaseIandIIresearch,wasmadetoincreasetaskduration(i.e.,theamountoftimeparticipantswererequiredto lookawayfromtheroad)withoutimposingexcessivecognitiveoverhead[2].Each of the five random numbers was presented for 472 ms. This duration, which wasapproximately37.1percent less than thatusedduringPhases I and II,was shortenough to

Figure3.6.HeadwaymonitorinstalledintheSV.

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stronglydiscourageglancesaway from thedisplay (i.e.,back toa forwardfacingviewof theroad)while still allowing each number to be easily observed and retained. Observing thenumbersrequiredtheparticipantfullyaverttheirforwardfacingviewfromtheroad.3.4 InstrumentationThe SVwas instrumentedwith two data acquisition systems, one for collecting inertial andhighlyaccurateGPSpositiondata,theotherformiscellaneousanalogdata.BothsystemswereinstalledintheSVtrunktominimizeparticipantdistractionduringtheexperimentaldrive.Themovingleadvehicle(MLV)wasequippedwithasimilarGPSenhancedinertialsensingsystemtofacilitaterealtimevehicletovehiclerange(e.g.,SVtoMLVheadway).TheballoonbasedSLVcontainednoinstrumentation.3.4.1 SubjectVehicleInstrumentationThebasicanalogmeasurementsloggedintheSVincludedbrakepedalforce,throttleposition,steeringwheelangle,brake linepressure,thestateofthevehicle,andvariousdata flags. Tomeasuretheforceappliedtothebrakepedal,aloadcellwasclampedontothefrontsurfaceofthepedal,asshowinFigure3.7.Tooffsetthedifferenceinstepheightimposedbyinstallationoftheloadcell,alightweightadapterwasattachedtothethrottlepedal.

Figure3.7.Loadcellusedtomeasurebrakeforce.Noteadaptertoincreasethrottlestepheight.Throttle position datawere collected through a direct tap of the vehicles throttle positionsensor (TPS). Under the dash, a potentiometer was attached to the steering column andconfiguredtomeasuresteeringwheelangle. Transducerswere installedatthebleederscrewofeachbrakecaliper tomeasurebrake linepressure. TheSVpositions,velocities, rotationalrates,andaccelerationsweremeasuredwithaGPSenhancedinertialplatforminstalledinthetruck, andwere resolved to the vehicles center of gravity (see Appendix C for a detaileddescriptionofthissystem).Finally,dataflagsindicatinginitiationoftherandomnumberrecalltask instructions,randomnumberrecalltaskduration,FCWonset,andthestateofeachFCWmodalitywererecorded.

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3.4.2 MovingLeadVehicleInstrumentationInamannersimilartothatusedfortheSV,theMLVpositions,velocities,rotationalrates,andaccelerationsweremeasuredwithaGPSenhanced inertialplatform. Although thisunitwasinstalled inthecabin,thesedatawerestillresolvedtothevehiclescenterofgravity. Usingawirelesscommunicationpackageintegratedwiththeinertialplatformsinstalledineachvehicle,thestateoftheMLVwasbroadcasttotheSV.TherelativepositionoftheMLVwithrespecttotheSV(i.e.,therealtimeheadway)wasoneofthesedatachannels.ToassisttheMLVdriverwithmaintainingthedesiredvelocities,aspeeddisplaywassecuredtotheinsideofthewindshield,justabovethedashboard.3.4.3 PresentationofAuditoryCommandsandAlertsAnautomatedsystemwasdevelopedtoproduceaudibleinstructionsandFCWalertsintheSVduringtheexperimentaltestdrive. Thissystemusedatrunkmounted laptopPCtoplay.wavfiles through a centermounted speaker installed in the SVs dashboard. Specifically, theinstruction,BeginTaskNow directedtheparticipanttobegintherandomnumberrecalltask.Softwareprovidedwith theaGPSenhanced inertialplatform installed in theSVwasused toautomaticallyinitiatepresentationoftheaudibleinstructionsandFCWusingpositionedbasedtriggerpoints.3.4.4 VideoDataAcquisition Foursmallvideocamerasweremounted inside thecabinof theSV toobservedriveractivityduring theexperimental testdrive. One camerawasmounted to theundersideof thedashnear the center console to record throttle and brake pedal activity. The pedals wereilluminatedbyalightstripcontaining20infraredLEDs.Asecondcamerawasmountedtotherearwindow interiortrimfacingforwardtoobservehowthedriverengagedwiththerandomnumberrecalltaskdisplay.Twocamerasweremountedtotherearviewmirror:(1)aforwardfacingcamerawasmountedtothebacksideoftheinteriorrearviewmirrortoobserveSVlanekeeping,SVtoMLVheadway,andhowtheSVapproachedtheSLVduringthefinalpassoftheexperimentaldrive,and (2)arearfacingcamerausedtoobservetheparticipants'eyeglanceactivity and physical reactions to the suddenly appearing SLV. A small microphone wasmountedintheinteriortrimabovethedrivershead.Themicrophonesignalwasamplifiedtoachievegoodreceptionofdrivercomments,experimentersinstructions,andFCWalertswhereapplicable.

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4.0 TESTPROTOCOL4.1 OverviewRealdrivers,ages25to55yearsold,wererecruitedfromthegeneralpublicforparticipationinthisstudy. Eachparticipantwasasked to follow theMLVwithin theconfinesofacontrolledtest course,while attempting tomaintain a constant headway, and instructed to perform aseriesoffourdistractiontasks intendedtobrieflydiverttheirattentionawayfromaforwardviewing position. With the participant fully distracted during the final task, theMLV wasabruptlysteeredoutofthetravellanetorevealarealisticlookingfullsizeballooncar,actingastheSLVintheimmediatepathoftheSV.AtanominalTTCof2.1sfromtheSV,oneofeightFCWalertswaspresentedtothedistractedparticipant. Themanner inwhich thedriver responded to theFCWalertwasused toassessdrivervehicle interface (DVI) effectiveness. The LeadVehicleCutOut scenario, as viewedfrom inside theSV, isshown inFigure4.1. Anexampleofa rearend impactwith theSLV isshowninFigure4.2.

Figure4.1.Leadvehiclecutoutscenario.

Figure4.2.Subjectvehicletostationaryleadvehicleimpact.

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4.2 ParticipantRecruitment

Participant recruitmentwas accomplished by publishing advertisements in local newspapersandonlineviaCraigslist. Intheseadvertisements,shown inAppendixD,prospectivesubjectswere instructed to contactNHTSAs VRTC if interested in study participation. RespondentswerescreenedtoensuretheysatisfiedthehealthandeligibilitycriteriadescribedinAppendixE.Ifthesecriteriaweresatisfied,therespondentswereprovidedwithadditionalstudydetails,andmorespecificpersonalinformationwascollectedfromthem.4.3 PrebriefingandInformedConsentMeetingUponarrivingatVRTC,participantsweregreetedandescorted toaconference room. Here,eachparticipantwasprovidedwithan informed consent formdescribing thepurposeof thestudytobeanevaluationofhowinterfacingwithanelectronicdevicemayaffecttheirabilitytomaintainaconsistentdistancebetweentheirvehicleandonebeingdrivendirectly infrontofthem.Theinformedconsentform,showninAppendixE,explainedthatawindshieldmounteddisplaywouldbeusedtoreportthedistancebetweenthetwovehicles(theheadwaymonitor),and that the study participants would be asked to interface with the electronic device (arandomnumberdisplay)fourtimesduringtheirtestdrive.4.4 VehicleandTestEquipmentFamiliarizationFollowingcompletionoftheprebriefing,participantswereescortedtotheGovernmentownedSV. Eachparticipantwas instructedtoturntheircellphoneoff,securetheirseatbelt,adjustthe seat and mirrors to comfortable positions, and to familiarize themselves with theorientationofthebasicvehiclecontrols(e.g.,throttle,brakepedal,turnsignalindicators,etc.).Participantsuseof sunglasseswhile in theSVwasnotallowed. An invehicleexperimenter,who sat behind the participant in the left rear seating position for the duration of theexperimental drive, described the location and functionality of the headway monitor andrandom number display to the participant, and asked that they be adjusted to insure acomfortable viewing position5. During this process, the invehicle experimenter describeddetailspertainingtothetwotypesoftasksbeingusedduringtheexperimentaldrive:headwaymaintenance and random number recall. Together, these tasks were ultimately used tofacilitatethechoreographydesignedtoevaluatehowtheparticipantsrespondedtothevariousFCWmodalitiesunexpectedlypresentedattheendoftheirdrive.4.4.1 MaintainingaConstantHeadwayForamajorityoftheirdrive,participantswereinstructedtomaintainaconstantdistanceof110ft between the front of their vehicle to the rear of theMLV being driven at 35mph. Themagnitude of this distance, or headway, was selected to best balance participant safety,

5 The attachment points of the headwaymonitor and random number displaywere not adjustable, only theviewingangles.

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participantcompliance (e.g., theirwillingness tomaintainacloseproximity to theMLV),andtheabilityof theMLV toeffectivelyobstruct theparticipantsviewaheadof it. Participantswerenotpermitted tousecruisecontrolwhileattempting tomaintainaconstantSVtoMLVheadway. However,participantswereencouragedtousetheheadwaymaintenancemonitordescribedinSection3.1.1toassistthemwiththistask.Althoughtheparticipantswereinstructedtomaintainaheadwayof110ftwhiledrivingonthestraightsectionsofthetestcourse(subsequentlyreferredtoasapass),theywerealsotoldthata toleranceof15 ft (i.e.,aheadwaybetween95 to125 ft)wasacceptable. If the invehicleexperimenterobserved that theactualheadwaywasoutsideof this rangeduring theexperimentaldrive,theparticipantwasremindedwhattheacceptableperformancewas,andencouraged to increase/decrease the SV speed to tighten/lengthen their following gap.Sustainednoncompliancewiththisrequestresulted inadeductionofthetask incentivepay,describedinSection4.5.2.4.4.2 RandomNumberRecallDuring each pass, participantswere instructed to complete a total of four random numberrecall tasks. Using the display previously shown in Figure 1.2, presentation of five randomnumberswas initiated 1.0 second after conclusion of the instruction to begin the randomnumberrecalltask,andapproximately77secondsafterestablishing lanepositiononthetestcourse(i.e.,theonsetofagivenpass).Tominimizevariability,therandomnumberrecalltaskinstruction andpresentationof the randomnumber recall tasknumberswere automaticallytriggered at the desired points on the test course using a GPSbased closedloop feedbackcontrolalgorithm.4.5 StudyCompensation4.5.1 BasePayTest subjects received a nominal compensation of $35.00 for participation in the study and$0.50permileforeachmiledrivenfromtheirresidencetothestudysite.4.5.2 IncentivePayToencouragegoodperformance,an incentiveschedulewasused foreachtask. Iftheywereable to maintain a consistent headway when instructed to do so, a factor critical tochoreography, participants received up to $20.00 more than their base pay. Specifically,participantsreceived$5.00perpass ifamajorityofthatpasswaswithinarangeof95125ft.This incentivewasawardedonapasstopassbasis;performanceobservedduringany singlepasshadnoinfluenceontheearningpotentialoftheotherpasses.If a participant successfully completed all aspects of the random number recall task, theyreceived an additional$45.00. This incentivewas larger than that associatedwithheadway

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maintenancesince itwas imperativetheparticipantsbefullydistractedaheadof(andduring)theLeadVehicleCutOutmaneuverandthesubsequentpresentationoftheFCWalert.Duringthe firstpass,participantswereawarded$1.50pernumbersuccessfullyrecalled in theorderpresented. For the second and third passes, participantswere awarded $2.50 per numbercorrectlyrecalled.DuetothepresenceoftheSLV,allparticipantsreceivedthemaximumtaskcompensation ($12.50), regardlessof taskperformance,during the finalpass. If thenumbersequence indicated by the participantwas not correct for a given pass, therewas a $1.00penaltyimposedforthetaskcompensationearnedduringthatpass.Table4.1summarizestheincentivepayscheduleused in thisstudy,AppendixGpresents the logsheetusedby the invehicleexperimentertotabulatetheparticipantsperformance.

Table4.1.TaskPaymentSchedule.

Pass#Headway

Maintenance

RandomNumberRecall

TaskBasedPaymentCorrect#Compensation

IncorrectOrderDeduction

1 $5ifwithinrange $1.50per#correct $1perordererror Totalforpass#1




TotalCompensation Sumofpasstotals

Throughout the experimental drive, the invehicle experimenter informed the participant oftheirtaskperformanceshortlyafterconclusionofthepassduringwhichthecompensationwasearned.Thisfeedbackwasusedtokeepparticipantsmotivated(e.g.,Youdidwellduringthatpass.), to indicatehow acceptable theirperformancewas (i.e.,howmuchof themaximumpaymentwasawarded),andtoprovideameansforsuggestinghowtaskperformancemaybeimprovedduringsubsequentpasses(e.g.,Yourheadwaywasabittoolongduringthelasttrial.Pleasetrytodriveclosertotheleadvehicleduringthenextpass.).4.6 PretestForwardCollisionWarningEducationandFamiliarizationNo pretest FCW education, familiarization, or instructionwas provided to the participantsrecruitedforthisstudy. Timeandbudgetaryconstraints,andthedesiretohaveareasonablenumberofparticipantspertestcondition,imposedalimitationthateitherallsubjectswould,orwouldnot,receiveinformationregardingFCWbeforetheexperimentaldrive.Soastoobservethemostgenuine,untrainedresponsestothevariousFCWmodalities,responsesnotartificiallyinfluenced by receiving statements or descriptions of an unfamiliar technology less than anhourbeforereceivingthealertduringtheirdrive,theauthorsoptedtoexcludeFCWeducationorfamiliarizationfromtheprotocolusedforthisstudy.

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4.7 FCWAlertModalitiesTable4.2providesa summaryof theeightFCWmodalitiesused in this study. Aspreviouslyexplained,thebasisfor includingthesealertswastwofold: prevalence incontemporaryFCWimplementationsandpositiveresultsfromthePhaseIstatictest.

Table4.2.FCWAlertModalitySummary.

FCWModality AlertOrigin

None Baseline(noalert)

VisualOnly 2008VolvoS80(HUD)

AuditoryOnly 2010MercedesE350(repeatedbeeps)

HapticSeatBelt 2009AcuraRL(reversibleseatbeltpretensioner)

Visual+Auditory 2008VolvoS80+2010MercedesE350

Visual+HapticSeatBelt 2008VolvoS80+2009AcuraRL

Auditory+HapticSeatBelt 2010MercedesE350+2009AcuraRL

Visual+Auditory+HapticSeatBelt 2008VolvoS80+2010MercedesE350+2009AcuraRL

4.8 TestCourseThe studys primary driving taskwas performed on Lane 4 of the Transportation ResearchCenter,Inc.(TRC)SkidPad.AnoverviewoftheSkidPadandthekeylogisticsassociatedwiththeexperimentaldesignisprovidedinFigure4.3.

Sincetheparticipantsweremembersofthegeneralpublic,exclusiveuseoftheentireSkidPadwasusedduringtheperiodsoftestconducttomaximizesafety.PerformingtestsontheSkidPad provided the subjectswith an opportunity to use significant avoidance steering, should

NorthLoop SouthLoop

Beginningoflanedelineations

Presentationofdistractiontaskwhensubjectvehicleisheadingnorth

Presentationofdistractiontaskwhensubjectvehicleisheadingsouth

Figure4.3.TRCSkidPaddimensionaloverview.

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theydeemitnecessary,withoutriskofaroaddepartureorimpactwithothervehicles,foreignobjects,etc.Testswereperformedduringdaylighthourswithgoodvisibility.4.9 ExperimentalTestDriveTheexperimentaldriveusedinthisstudybeganandconcludedwiththeSVandMLVstagedinaVRTC parking lot. Following the vehicle and test equipment familiarization, and taskorientation,theinvehicleexperimenterindicatedtheleadvehicletotheparticipant(i.e.,theMLV),and instructed them to follow it to the testcourse. Thebriefdrive to the testcoursefromVRTCwasperformedat25mph,10mph lessthanthatspecifiedforavalidstraightlinepassduringtheexperimentaldrive.Thelowspeedoftheprestudydriveservedtwopurposes:(1)toincreasetheparticipantsfamiliarizationwiththeheadwaymonitoroperationinabenignoperating condition, and (2) to give the participant an opportunity to practice the task ofmaintainingadesiredheadwaytotheMLVinanonthreateningenvironment.4.9.1 Pass#1of4Following their test vehicle and equipment familiarization, the invehicle experimenterinstructed theparticipants toestablishpositiononSkidPadLane4,headingsouth, followingtheMLVwithaheadwayof110ftusingthewindshieldmountedheadwaymonitorasaguide.Atalocationapproximately0.75milesfromthepointwherelanepositionwasfirstestablished,andwhiletheparticipantwasdriving,theparticipantwasautomaticallyinstructedtobegintherandomnumberrecalltaskwhenpromptedbyaprerecordedmessageplayedthroughtheSVaudiosystem.Asdescribedinthetaskorientation,oncethefifthnumberhadbeenpresented,thesubjectwastotelltheinvehicleexperimenterwhatfivenumberswereshownintheordertheywerepresented. Aftercompletingthefirstrandomnumberrecalltask,participantswereinstructedtocontinuefollowingtheMLVaroundtheSkidPadssouthcurve.Afteremergingfromthecurveheadingnorth, theywere told to follow theMLVback into Lane4headingnorth, and reestablish anominalheadwayof110ftusingthewindshieldmounteddistancedisplayasaguide.4.9.2 Pass#2of4After approximately 0.75miles from the pointwhere lane position heading northwas firstestablished,theparticipantwasautomaticallyinstructedtobegintheirsecondrandomnumberrecalltask.Asbefore,thetaskwasdeemedcompleteoncethesubjecthadtoldtheinvehicleexperimenterwhatfivenumberswereshown,intheordertheywerepresented.Aftercompletingthesecondrandomnumberrecalltask,theinvehicleexperimenteri

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