Georgia Express Lane Corridors Vehicle Occupancy and Throughput Study 2018-2020: Volume I: Vehicle and Person Throughput Analysis Before and After the I-75 Northwest Corridor and I-85 Express Lanes Extension

Guensler, Randall; Liu, Haobing; Lu, Hongyu; Chang, Chia-Huai; Dai, Ziyi; Xia, Tian; Fu, Zixiu; Liu, Diyi; Kim, Daejin; Zhao, Yingping; Guin, Angshuman · 2022 · ROSA P / Georgia Institute of Technology. School of Civil and Environmental Engineering

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 study evaluates the impact of new Express Lane facilities in Atlanta, Georgia, on vehicle and person throughput. Conducted by the Georgia Institute of Technology for the State Road and Tollway Authority (SRTA), the research addresses the need for ongoing performance monitoring to ensure infrastructure investments yield desired returns. Specifically, it analyzes changes in travel behavior, vehicle activity, and person throughput (calculated as vehicle flow multiplied by occupancy) following the opening of the I-75 Northwest Corridor (NWC) and the I-85 Express Lanes Extension. The study covers four managed lane corridors: the NWC (I-75/I-575), the existing I-85 Express Lanes, the I-85 Extension, and the I-75 South Metro Express Lanes. The methodology employed a before-and-after design comparing baseline data from 2018 with post-opening data from 2019. Vehicle throughput was measured using automated machine vision systems, including GDOT’s Georgia NaviGAtor and SRTA’s monitoring systems, with rigorous quality assurance to filter outliers. Vehicle occupancy data were collected through large-scale roadside observational field studies across general purpose and Express lanes. The researchers utilized regression tree analysis to identify and control for potential data collector bias and other variables affecting occupancy, such as lane position and time of day. The study also accounted for high-occupancy modes, including express buses and vanpools, to ensure accurate person throughput calculations. Key findings indicate that between 2018 and 2019, average vehicle occupancy decreased while traffic volumes increased significantly. Despite the drop in occupancy, person throughput increased at all sites due to the substantial rise in vehicle counts. On the I-85 corridor, vehicle throughput rose by 5–7% in the morning peak and ~10% in the evening peak, with person throughput increasing by 1–2% and 5%, respectively. The NWC saw more dramatic changes: vehicle throughput on I-575 increased by over 35% in both peak periods, and I-75 saw similar increases in the morning peak. This surge was attributed to the diversion of commute traffic from arterials to the freeway as congestion declined. The increase in vehicle throughput was driven primarily by an influx of single-occupant vehicles, which reduced the overall carpool mode share, even though the absolute number of carpools on I-575 increased slightly. The study concludes that the opening of Express Lanes successfully increased both vehicle and person throughput, validating the infrastructure's role in managing congestion and attracting diverted traffic. However, the reliance on single-occupant vehicles highlights a shift in travel behavior that reduces the relative share of carpools. These results provide critical data for transportation planners to assess the effectiveness of managed lanes and understand the trade-offs between increased capacity and mode composition. The rigorous data collection and bias-control methods established in this report offer a robust framework for future performance assessments of similar transportation facilities.

Key finding

The opening of Express Lane facilities led to significant increases in both vehicle and person throughput across all studied corridors, primarily driven by a large influx of single-occupant vehicles that offset the observed decrease in average vehicle occupancy.

Methodology

field_study

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