Atlanta I-85 HOV-to-HOT Conversion: Impacts On Weaving And Effective Capacity

The purpose of this paper is to identify changes in effective capacity and weaving before and after the conversion of an HOV lane to an HOT lane. Vehicle speed and count data was extracted from the GDOT video-detection system (VDS), and lane changes were extracted from footage recorded from pan-tilt-zoom (PTZ) cameras along the corridor. Speed-density and speed-flow plots are generated for each of the three periods of the conversion. Two methods for estimating the effective capacity and speed corresponding to that capacity are presented. Although conclusions are not definitive, the effective capacity and the speed of the managed lane increase after the conversion (HOT operation). Smaller increases in effective capacity and speed are noted for the left-most general purpose lane after the conversion took place. A second analysis assesses the impact of weaving activity on HOT speeds. A linear regression indicates that before the conversion, general purpose lane speeds had the greatest impact in estimating the HOV lane speed. The density of lane changes into and out of the HOT lane did not show up as a significant variable. However, after HOT operations began, weaving density did show up as a significant variable, albeit still less significant than general purpose speed. This is likely due to the fact that the managed lane is now priced (decreasing the correlation between the speed of the general purpose lanes and HOT lane) and enforcement heavily discouraging illegal use of the lane. Weaving density appearing as a significant variable in explaining HOT speed warrants further investigation that may lead to more conclusive results.