Intelligent Cruise Control Field Operational Test Vol III: Performance of a String or Cluster of ACC-Equipped Cars

Bogard, S.; Fancher, Paul; Ervin, Robert D.; Hagan, Michael · 1998 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

archive: archived pipeline: cataloged verified

Get this paper ↗ (full text — opens at the source; we link to it, we don't host it)

Summary

This report, Volume III of the Intelligent Cruise Control (ICC) Field Operational Test, investigates the performance and traffic impact of serial strings or dense clusters of passenger cars equipped with Adaptive Cruise Control (ACC). The study was motivated by the expectation that high penetration rates of ACC technology would lead to frequent string or cluster formations on public roadways. The primary objective was to evaluate the safety, traffic flow implications, and potential interference with unequipped vehicles resulting from multiple ACC-equipped cars operating in close proximity. The research aimed to expose practical issues associated with ACC string operations in naturalistic traffic settings, rather than demonstrating theoretical string stability, which was known to be absent in the elementary ACC systems used. The experimental design involved eight ACC-equipped vehicles driven by experienced researchers on limited-access freeways in southeast Michigan during moderate to light traffic conditions. Three distinct test scenarios were conducted: longitudinal string tests with four and eight vehicles, and cluster tests with eight vehicles. In the string tests, drivers attempted to maintain specific formations with headway times of 1.0 or 1.4 seconds. The four-vehicle tests focused on longitudinal performance and disturbance handling, while the eight-vehicle tests examined formation difficulty, stability, and effects on surrounding traffic on both two-lane and three-lane highways. The cluster tests involved dispatching vehicles at intervals to observe spontaneous grouping without deliberate string formation instructions. Data were collected on vehicle velocity, range, and range-rate, alongside driver observations regarding ease of formation and traffic interactions. The results demonstrated that maintaining deliberate strings was difficult and unnatural, particularly for eight-vehicle formations. In the four-vehicle string tests, longitudinal disturbances introduced by the lead vehicle propagated down the string, causing exaggerated velocity overshoots and undershoots in trailing vehicles. In one instance, the third and fourth vehicles required driver intervention via braking to avoid collisions due to insufficient control authority to handle the disturbance. The eight-vehicle string tests revealed that steady-state conditions were rarely achieved on two-lane highways due to interference from other traffic. Rearmost vehicles experienced continuous oscillations and significant speed changes. On three-lane highways, strings were more stable but still caused severe transients when disturbed. Crucially, the study found that ACC strings, especially those with 1.0-second headways, significantly impeded cross-lane movements for other drivers, including trucks attempting to change lanes. The 1.4-second headway allowed for more cut-ins but still presented challenges. Cluster tests showed that vehicles tended to group together, but without the anomalies of forced string formation. The significance of these findings lies in the identification of practical limitations and traffic conflicts associated with ACC technology. The study concludes that while ACC can handle routine disturbances, it lacks the stability to manage significant longitudinal perturbations in long strings without driver intervention. Furthermore, the presence of ACC strings can disrupt normal traffic flow by impeding lane changes and frustrating other motorists, particularly heavy vehicles. These insights are critical for future product design and public policy, suggesting that ACC systems may need enhancements to improve string stability and reduce interference with unequipped traffic. The report also highlights the importance of considering sociological expectations and traffic dynamics in the development of automated highway systems.

Key finding

Elementary ACC-equipped vehicle strings exhibit instability where longitudinal disturbances amplify down the line, causing rear vehicles to experience exaggerated velocity changes and reduced headways that often require manual driver intervention.

Methodology

field_study

Sample size: 8

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).

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

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• traffic density
• following distance