Human Factors Aspects of the Transfer of Control from the Driver to the Automated Highway System

Bloomfield, John R.; Buck, J.R.; Christensen, J. M.; Yenamandra, A. · 1995 · ROSA P / United States. Department of Transportation. Federal Highway Administration

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Summary

This study investigates the human factors involved in transferring vehicle control from a driver to an Automated Highway System (AHS). Specifically, it examines how drivers safely enter an automated lane and hand over control without disrupting the flow of automated traffic. The research addresses a generic AHS configuration consisting of a three-lane freeway where the left lane is reserved for automated vehicles traveling in strings, while the center and right lanes remain under manual driver control. Unlike previous studies that focused on exiting the automated system, this experiment focuses on the entry maneuver, motivated by the need to determine conditions that minimize interference with automated traffic flow. The experiment utilized the Iowa Driving Simulator, featuring a moving base platform and a mid-sized sedan, with 24 drivers aged 25 to 34. Participants drove from an entry ramp into the unautomated lanes and, upon receiving an "Enter" command, merged into the automated lane. The study employed a factorial design manipulating three variables: the method of control transfer (manual button press vs. partially automated detection of lane crossing), the design velocity of the automated lane (104.7, 128.8, or 153.0 km/h), and the inter-string gap between automated vehicle strings. Key performance metrics included entering response time, lane-change time, entering exposure time, string-joining time, and potential time delays caused to the automated string. Results indicated that the required minimum inter-string gap increased significantly with higher design velocities. For a design velocity of 104.7 km/h, the minimum gap was 1.14 seconds, whereas for 153.0 km/h, it rose to 7.33 seconds. Consequently, the hourly traffic capacity for the automated lane was substantially higher at lower speeds; the capacity at 104.7 km/h was estimated to be four times greater than at 153.0 km/h. This reduction in capacity at higher speeds was attributed to the larger velocity differential between the unautomated lane speed limit and the automated design velocity, which necessitated longer gaps for safe merging and acceleration. No collisions occurred during the trials, and questionnaire data suggested drivers felt safe and maintained control during the entry maneuver. The findings imply that lower design velocities for automated lanes may yield higher overall system efficiency due to reduced spacing requirements between vehicle strings. The study concludes that the method of transferring control and the size of the inter-string gap significantly influence driver performance and system capacity. These results provide critical data for engineers designing Intelligent Transportation Systems, highlighting the trade-offs between high-speed automation and traffic throughput efficiency.

Key finding

Hourly traffic capacity at a design velocity of 104.7 km/h is likely four times greater than at 153.0 km/h because the required minimum inter-string gap time increases from 1.14 seconds to 7.33 seconds as velocity rises under the partially automated transfer method.

Methodology

simulator

Sample size: 24

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• automation
• takeover transitions
• manual
• automation surprise
• situational awareness
• work zones

Information type

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• Empirical Findings: behavioral performance data
• Methodological Resource: measurement protocol
• Theoretical Contribution: computational model