Evaluation of the Impact of the I-66 Active Traffic Management System: Phase II

About the report:

In early 2013, construction began on a Virginia Department of Transportation (VDOT) project to install an Active Traffic Management (ATM) system on I-66 from US 29 in Centreville to the Capital Beltway (I-495). Construction was completed in September 2015. This project was intended to improve safety and operations on I-66 without physically expanding the roadway through better management of the existing facility. The main components of the installed system included advisory variable speed limits (AVSL), lane use control signals (LUCS), and hard shoulder running (HSR).

In 2016, the Virginia Transportation Research Council completed a Phase I evaluation of the system, covering its first 5 months of operation. A before-after study to quantify the effectiveness of the system was performed using “after” data from October 2015–February 2016 (21 weeks) for the operational analysis and data from October 2015–December 2015 (13 weeks) for the safety analysis. Since the operational and safety analyses were performed using limited amounts of data, the results were preliminary. The analysis showed several benefits attributable to dynamic HSR, but only 1.5 months of data were available with the AVSL active.

In Phase II, the project was expanded to evaluate the long-term effects of the I-66 ATM system. For this phase, data from October 2015–November 2017 were used for the operational analysis and data from October 2015–December 2016 were used for the safety analysis. The operational measures of effectiveness were the same as for Phase I and included the ATM utilization rate, average travel time, and travel time reliability. In order to evaluate the safety impacts, the empirical Bayes method was used with safety performance functions developed for Virginia. Segment-level analysis was performed to determine the segments that had benefitted the most from the implementation of the ATM system. From this segment-level analysis, it was determined that HSR was the ATM component that created most of the improvements on I-66.

The operational analysis showed that travel time improved significantly during off-peak hours after the ATM system was activated but that travel time during peak periods in the peak direction of travel generally did not improve. Further analysis revealed that most of these improvements occurred on the sections with HSR. The safety evaluation showed 6%, 10%, and 11% reductions in total (all severity), multiple-vehicle (all severity), and rear-end (all severity) crashes, respectively. Segment-level analysis again showed that the most safety benefits were found for locations with HSR (crash reductions of 25% to 40%), and no statistically significant reductions were found for sections with only AVSL and LUCS. The results of the analysis showed that HSR could produce statistically significant operational and safety benefits but that the effects of other ATM components were more limited. The study recommends that VDOT’s Operations Division and regions use the results from I-66 to inform decisions about future ATM and HSR use in Virginia.

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