HOV to HOT Conversion Impacts on Carpooling

Guensler, Randall; Ko, Joonho; Kim, Daejin; Sheikh, Adnan; Khoeini, Sara; Xu, Yanzhi · 2016 · ROSA P / National Center for Transportation Systems Productivity and Management (U.S.)

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Summary

This study investigates the factors influencing drivers’ choices regarding High-Occupancy Toll (HOT) lane use and carpooling following the conversion of High-Occupancy Vehicle (HOV) lanes to HOT lanes on the Atlanta I-85 corridor. The research addresses a critical gap in transportation planning: while HOT lanes are increasingly deployed to manage congestion, their impact on carpool formation and driver behavior varies by facility characteristics. Previous studies relied on marketing data, which lacks direct insight into driver perceptions and specific trip patterns. This study aims to provide a comprehensive understanding of these behavioral changes to inform future HOT policy and operations. The researchers employed a self-administered mail-out/mail-back survey targeting households identified through license plate data collected before and after the 2011 HOT lane installation. Although the initial retrieval rate was low (5.4%) and data screening reduced the usable sample significantly due to missing values and inconsistencies, the final datasets included 313 valid cases for HOT lane choice analysis and 332 for carpool choice analysis. The survey captured socioeconomic demographics, commute characteristics (distance, work start time), and perceptions of whether HOT lanes improved commute conditions. The analytical approach utilized classification trees to identify key variable interactions and logistic regression models to quantify statistical significance and odds ratios for binary choices (HOT vs. General Purpose lanes; Carpool vs. Drive Alone). The results indicate that driver perception of HOT lane effectiveness is the strongest predictor of lane choice. Commuters who perceived that HOT lanes improved their commute were approximately 11 times more likely to use them. Socioeconomic factors also played a role; commuters in their 40s, those with higher incomes, and those with higher education levels were more likely to choose HOT lanes, suggesting a higher value of time among these groups. Longer commute distances also correlated with increased HOT lane usage. Regarding carpooling, the study found that carpool breakups outpaced formation, with 89% of post-conversion carpoolers being former carpoolers. Crucially, commuters with a positive perception of HOT lanes were less likely to carpool, implying that improved HOT performance may discourage carpool formation. Former carpool status was the dominant factor in carpool choice models. The findings suggest that HOT lane operators must maintain high performance levels to maximize lane utilization, as driver perception drives adoption. However, the inverse relationship between positive HOT perception and carpooling indicates that HOT installations do not inherently boost carpooling and may even disrupt existing carpools. Policymakers are advised to develop strategies that simultaneously improve HOT operations and encourage carpool formation, rather than assuming HOT lanes will naturally increase high-occupancy vehicle usage. The study highlights the importance of considering driver perception and socioeconomic characteristics in designing effective managed lane policies.

Key finding

Drivers' perception of HOT lane effectiveness is the dominant factor in lane choice, while former carpoolers remain the primary source of current carpoolers, indicating that HOT installations do not necessarily increase overall carpooling rates.

Methodology

survey

Sample size: 332

Provenance

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

Topics

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• traffic density