Collection, Screening, and Evaluation of Vehicle Occupancy Data

Abstract

In 2008, the Georgia State Road and Tollway Authority and the Georgia Department of Transportation successfully applied to the U.S. Department of Transportation for seed funding under the Congestion Reduction Demonstration Program Grant to convert the congested I-85 high-occupancy-vehicle (HOV) lane to a high-occupancy-toll (HOT) lane. The facility was converted into a HOT lane and opened on October 1, 2011. This paper reports on the collection, processing, and filtering of the vehicle occupancy data and the factors that influenced vehicle occupancy along the I-85 corridor both before and after the conversion. The research effort used regression tree analysis techniques to identify data collector bias and then the effects of different factors such as season, data collection site, morning peak–evening peak, and lane type on vehicle occupancy. The study found that vehicle occupancy data on Monday were different from those data collected on Tuesdays, Wednesdays, and Thursdays. The study identified data collectors and sessions that had statistically different data from other sessions and filtered those data. The research effort then explored the factors affecting vehicle occupancy for the morning peak and the afternoon peak periods separately, given that related travel behavior characteristics were quite different. The research identified lane type (managed or general-purpose) as the most significant factor affecting occupancy, followed by pre- and postconversion of the HOV lane to HOT lane. The study also found that average vehicle occupancy decreased after conversion of the HOV lane. On the basis of the results of this study, the vehicle occupancy data were aggregated into the center stations, north of the GA-316 region and south of the I-285 region. The vehicle occupancy data are currently being applied to evaluate person throughput along the corridor.