REPORT

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Publication Number: FHWA-HRT-17-024 Date: June 2017

Publication Number: FHWA-HRT-17-024
Date: June 2017

Cooperative Adaptive Cruise Control Human Factors Study: Experiment 4—Preferred Following Distance and Performance in An Emergency Event

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FOREWORD

This report presents human factors research to examine the effects of cooperative adaptive cruise control (CACC) on driver performance in a variety of situations. It summarizes driving simulator experiments in which the driver was required to drive in a stream of vehicles. Participants experienced a vehicle merge in front of them as well as an emergency event that required driver intervention. The participants’ preferred following time gap did not significantly affect collision avoidance. However, those participants following at shorter distances were more likely to intervene more rapidly that those following at a far distance.

These findings support the idea that performance depends more on overall CACC following distance settings than with drivers’ personal preferences. This will allow CACC systems to implement a single following distance gap (or set of gaps based on vehicle physics). The results show that it is critical that drivers receive clear alerts when it is necessary to take over control of the vehicle. Without such measures, it is possible that CACC implementation may not result in improved roadway safety. This report should be useful to transportation professionals, State transportation departments, and researchers interested in the effects of automation on driver behavior and performance.

Monique R. Evans, P.E.
Director, Office of Safety
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

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Technical Report Documentation Page

1. Report No. FHWA-HRT-17-024	2. Government Accession No.		3 Recipient's Catalog No.
4. Title and Subtitle Cooperative Adaptive Cruise Control Human Factors Study: Experiment 4—Preferred Following Distance and Performance in an Emergency Event			5. Report Date June 2017
			6. Performing Organization Code
7. Author(s) Stacy A. Balk, Steven Jackson, and Brian H. Philips			8. Performing Organization Report No.
9. Performing Organization Name and Address Leidos, Inc. 6300 Georgetown Pike McLean, VA 22101-2296			10. Work Unit No. (TRAIS)
			11. Contract or Grant No. DTFH61-13-D-00024
12. Sponsoring Agency Name and Address Office of Safety Research and Development Federal Highway Administration 6300 Georgetown Pike McLean, VA 22101-2296			13. Type of Report and Period Covered Final Report: December 2013–July 2016
			14. Sponsoring Agency Code HRTM-30
15. Supplementary Notes The Contracting Officer’s Representative was David Yang (HRDS-30), and the Government Task Manager was Brian Philips (HRDS-30).
16. Abstract This study is the fourth in a series of four experiments exploring human factors issues associated with the introduction of cooperative adaptive cruise control (CACC). Specifically, the goals of this experiment were as follows: Assess drivers’ workloads under two different CACC following gaps (near and far). Assess drivers’ reactions to a vehicle merging in front of them under different following gaps. Assess drivers’ reactions to an emergency event that requires driver intervention to avoid collision. Determine whether preferred time gap following distance affects the first three goals. As measured by the National Aeronautics and Space Administration Task Load Index, drivers’ perceived workloads did not vary between the cruise period and after the vehicle merge. However, workloads were significantly greater after the emergency crash event. Workloads varied based on neither assigned following distance nor preferred following distance. Those participants in driving in the assigned near distance were more likely to hover their foot over the brake during the merging event and to react faster to the emergency event. Preferred following distance did not affect performance. Throughout the study, participants’ following distance preferences did not affect performance. In other words, one’s abilities may not necessarily reflect his or her following preferences. This finding is promising for widespread implementation of CACC.
17. Key Words Cooperative adaptive cruise control, CACC, human factors, driving simulation, attention, distraction		18. Distribution Statement No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161. http://www.ntis.gov
19. Security Classification (of this report) Unclassified	20. Security Classification (of this page) Unclassified		21. No. of Pages 27	22. Price N/A

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Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

CHAPTER 1. INTRODUCTION

CHAPTER 2. PART 1

CHAPTER 3. PART 2

CHAPTER 4. DISCUSSION

ACKNOWLEDGEMENTS

REFERENCES

LIST OF FIGURES

Figure 1. Graph. Mean NASA-TLX scores by preferred time gap, assigned time gap, and assessment location

Figure 2. Graph. Time (s) from principal other vehicle entering the traffic flow to participant brake pedal onset based on preferred and assigned time gaps

Figure 3. Graph. Probability of experiencing a crash based on both preferred and assigned following time gap

LIST OF TABLES

Table 1. Participant following time gaps (s) by speed during comfortable following drive

Table 2. Participant following time gaps (s) by speed during close following drive

Table 3. Participant following distance group assignments

Table 4. Total number of participants included in each condition

Table 5. Participant following time gaps (s) by speed during comfortable following drive in part 2

Table 6. Participant following time gaps (s) by speed during close following drive in part 2

Table 7. The time from merging vehicle entrance into lane until brake press

Table 8. Total number of crashes by preferred and assigned gaps

Table 9. Total number of non-crashes by preferred and assigned gaps

LIST OF ABBREVIATIONS

CACC	cooperative adaptive cruise control
LCD	liquid crystal display
NASA-TLX	National Aeronautics and Space Administration Task Load Index
SSQ	simulator sickness questionnaire

Page Owner: Office of Research, Development, and Technology, Office of Safety, RDT

Topics: research, safety
Keywords: research, safety, Cooperative adaptive cruise control, CACC, human factors, driving simulation, attention, distraction
TRT Terms: research, Safety and security, Safety, Transportation safety
Scheduled Update: Archive - No Update needed

This page last modified on 10/26/2018