Georgia Express Lane Corridors Vehicle Occupancy and Throughput Study 2018-2022

State Road and Tollway Authority 2021 Peach Pass Customer Satisfaction Survey

The primary objective of this research was to assess customer perceptions of, and satisfaction with, Peach Pass service and the Express Lane projects in Metro Atlanta, with respect to account registration, account management, customer service, and the performance and user experience associated with use of the Express Lane corridors. The survey also examined customers’ daily travel patterns, assessed changes in customer use of the Express Lanes due to the COVID-19 pandemic, and collected demographic information for crosstab assessment of facility use and customer satisfaction. These survey results allow SRTA to assess changes in customer service by comparing results to similar surveys conducted in 2012, 2014 and 2017. Ultimately, the insights derived from this research will help to improve internal processes that contribute to operational effectiveness, efficiency, and improved customer experience.

Volume I: Vehicle and Person Throughput Analysis: Before and After the I-75 Northwest Corridor and I-85 Express Lanes Extension

Ongoing assessment of system performance monitoring is critical to successful and efficient transportation planning, ensuring that infrastructure investments provide a desired return on investment. As with any new transportation facility, it is important to understand how Express Lane facilities affect travel behavior, resulting on-road vehicle activity, and subsequent person-throughput (a function of vehicle occupancy) as part of the facility performance assessment. This report summarizes the vehicle and person throughput analysis for the I-75 Northwest Corridor (NWC) and I-85 Express Lanes in Atlanta, GA, undertaken by the Georgia Institute of Technology research team for the State Road and Tollway Authority (SRTA). The research team tracked changes in observed vehicle throughput on four managed lane corridors and collected vehicle occupancy (persons per vehicle) data to assess changes in both vehicle throughput and person throughput associated with the opening of new Express Lane facilities. The team collected traffic volumes by video observation (GDOT’s Georgia NaviGAtor machine vision system and SRTA’s vehicle activity monitoring system). The team implemented a large-scale data collection effort for vehicle occupancy across all general purpose freeway lanes and from SRTA’s Express Lanes over a two-year period (before-and-after the opening of the Express Lanes). Between the baseline year (2018) and post-opening year (2019), the team observed a decrease in average vehicle occupancy (persons/vehicle), coupled with a significant increase in traffic volumes, especially on the NWC. The combined effect of increased traffic volumes and decreased occupancy still led to an overall increase in person throughput at all sites. Vehicle throughput on the I-85 corridor increased by about 5-7% and person throughput increased by 1-2% in the morning peak, and increased by around 10% for vehicles and 5% for persons in the evening peak. Vehicle throughput increased by more than 35% on I-575 in the AM and PM peaks, and by the same on I-75 in the AM peaks (only minor increases were noted in the PM peaks), likely due to the diversion of commute traffic from arterials onto the freeway corridor once the Express Lanes opened and congestion declined. Based upon vehicle throughput and occupancy distributions, the largest share of the increase in vehicle throughput in the peak periods came from an influx of single-occupant vehicle activity onto the corridor. Even though the number of carpools traversing the I-575 corridor increased slightly during the morning peak, the overall carpool mode share (percentage of carpools) decreased after the significantly greater numbers of single-occupant vehicles began using the corridor.

Volume II: Commutershed and Demographic Analysis: Before and After the I-75 Northwest Corridor and I-85 Express Lanes Extension

The research presented herein is part of the larger effort undertaken by the Georgia Institute of Technology research team to assess changes in vehicle and person throughput for Express Lane corridors in the Atlanta, GA metropolitan area between 2018 and 2020 (presented in Volume 1 of this report). Volume II presents the analytical results for morning and evening peak period geographic commutersheds and commuter demographics for I-75/I-575 Northwest Corridor (NWC) and I-85 Express Lane Corridor (from Indian Trail/Lilburn Road to Hamilton Mill Road). The team used license plate data collected during the study to identify the home ends of trips, and licensed household-level commercial marketing data for paired demographic data. These data were collected pre-and-post opening of two new and extended Express Lane corridors. The team observed changes in the geographic commutersheds (presented as 68% and 95% directional ellipses) and quantified changes in the user demographic characteristics on the general purpose (GP) lanes and the Express Lanes over time. Express Lane commutersheds tend to be more spatially concentrated near the facility than the GP lane commutersheds. Demographic analyses indicate that all income groups use the Express Lanes, and a larger percentage of higher-income households switched from GP lanes to Express Lanes when they opened. The distribution of ethnicity and household size follow the same trend as household income, which is not surprising given the correlation between income and ethnicity, and between income and household size. The team also retrieved morning peak-period commuter travel paths from the Atlanta Regional Commission’s (ARC’s) activity-based travel demand model (ABM) using path retention algorithms and compared model-predicted trips traversing the dedicated Express Lane entry ramp at Roswell Road and I-75 to field-observed trips data. Analyses revealed substantial differences between model-predicted trips and trips derived from license plate observations. The team observed more trips from neighborhoods located immediately to the southeast of the dedicated ramp than were predicted by the model. The demographic comparisons indicate that ABM travel demand model is predicting much higher fractions of middle-income households ($50,000 to $100,000), and households with three or more persons than are indicated by field observations. More higher-income households and smaller households use the facility than the model predicts. Results indicated that researchers should consider updating travel demand model algorithms used to predict Express Lane demand.

Atlanta I-85 HOV-to-HOT Conversion: Analysis of Vehicle and Person Throughput

This report summarizes the vehicle and person throughput analysis for the High Occupancy Vehicle to High Occupancy Toll Lane conversion in Atlanta, GA, undertaken by the Georgia Institute of Technology research team. The team tracked changes in observed vehicle throughput on the corridor and collected average vehicle occupancy (persons/vehicle) data to assess changes in person throughput. Traffic volumes were collected by VDS systems on the Georgia NaviGAtor system and the team implemented a large scale quarterly data collection effort for vehicle occupancy across all travel lanes. Between the baseline year (2011) and HOT implementation year (2012), significant changes were noted in both the vehicle and person throughput on the corridor at Center Way. Vehicle throughput on the I-85 HOT corridor decreased by about 6.6% (2698 vehicles) during the morning peak period, but only by about 2.9% (1148 vehicles) during the afternoon peak period. Average vehicle occupancy (persons/vehicle) also decreased during the same period. Reduced vehicle throughput and decrease in observed vehicle occupancy had a synergistic impact on estimated corridor person throughput, which declined significantly at a much faster rate than vehicle throughput. While traffic volumes declined by 6.6%, person throughput concurrently declined by about 9.9% (4868 individuals). While traffic volumes declined by approximately 2.9% in the afternoon peak period, person throughput concurrently declined by about 6.3% (3123 individuals). The data reveal that the majority of two-person carpools have been diverted from the HOV lane into the general purpose lanes after HOT lane implementation. Based upon vehicle throughput and occupancy distributions, the largest reduction in vehicle throughput in both the morning and afternoon peak periods came from a reduction in carpools (HOV2 and HOV3+ vehicles). Carpool mode share declined by more than 30% in the AM peak and by 25% in the PM peak, and average managed lane vehicle occupancy decreased from approximately 2.0 persons/vehicle to approximately 1.2 persons/vehicle.