Developing Analysis, Modeling, and Simulation Tools for Connected Automated Vehicle Applications: A Case Study on SR 99 in California

Liu, Hao; Lu, Xiao-Yun; Shladover, Steven E.; Huang, Zhitong · 2021 · ROSA P / United States. Federal Highway Administration

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Summary

This report documents a simulation-based case study investigating the effectiveness of SAE Level 1 automation, specifically Cooperative Adaptive Cruise Control (CACC), in mitigating congestion, fuel consumption, and emissions. The study focuses on a 13-mile northbound segment of State Route 99 in California, a corridor characterized by severe morning peak-hour congestion caused by interacting bottlenecks. The research was motivated by the need to quantify real-world benefits of Connected Automated Vehicle (CAV) technology, as high market penetration rates required for empirical observation are not yet available. The researchers employed microscopic traffic simulation models calibrated with field data from the study corridor and real-world CACC trajectory data. The modeling framework integrated a human-driver model with ACC and CACC car-following algorithms. The study evaluated four implementation strategies across various CACC market penetration rates (0% to 100%), traffic demand levels (baseline and a 20% increase), and management strategies, including Vehicle Awareness Devices (VADs) for manually driven vehicles and dedicated CACC Managed Lanes (MLs). Performance measures included average vehicle speed, fuel efficiency (miles per gallon), average string length, and the probability of CACC vehicles operating in strings. Key findings indicate that average corridor speed increased linearly with CACC penetration, rising by 70% (from 34 to 56 mph) at 100% penetration compared to the baseline. Fuel efficiency peaked at 26 mpg (a 5% improvement over baseline) at 30% CACC penetration but declined to 22 mpg at 100% penetration due to higher operating speeds. While CACC increased corridor capacity by approximately 30% at full penetration, this was significantly lower than the theoretical 90% capacity increase observed at isolated bottlenecks, suggesting that upstream improvements can cause downstream mobility reductions. Furthermore, even at 100% CACC penetration, the string probability remained only 80%, indicating a need for systematic string formation strategies. The VAD strategy improved string probability and speed at low-to-medium penetration rates, whereas the ML strategy alone decreased corridor performance by disrupting general-purpose lane traffic through merging maneuvers. The study concludes that while CACC offers significant mobility and environmental benefits, its effectiveness is limited by string formation challenges and corridor-level flow dynamics. The results highlight the necessity for coordinated traffic flow management strategies, such as speed harmonization, to balance input and output flows across bottlenecks. Additionally, the findings suggest that local or systematic string strategies are required to maximize the benefits of CACC technology, particularly in mixed-traffic environments.

Key finding

Average corridor speed increased by 70 percent at 100 percent CACC market penetration, while fuel efficiency peaked at 30 percent market penetration before declining at higher rates.

Methodology

simulator

Provenance

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

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• traffic density