Evaluation of the Impact of the I-66 Active Traffic Management System

About the report:

Construction of a Virginia Department of Transportation project to install an Active Traffic Management (ATM) system on I-66 from U.S. 29 in Centreville to the Capital Beltway (I-495) was completed in September 2015. The project was constructed to improve safety and operations on I-66 through better management of existing roadway capacity. The main components of the ATM system were advisory variable speed limits (AVSL), queue warning systems (QWS), lane use control signs (LUCS), and hard shoulder running (HSR).

Since ATM is still a relatively new approach in the United States, there was a need to analyze the effects of the I-66 ATM. Thus, a before-and-after study was conducted to quantify its effectiveness. The study used “after” data from October 2015-February 2016 (21 weeks) for the operations analysis and data from October 2015-December 2015 (13 weeks) for the safety analysis. Operations and safety evaluations were performed using limited data, so the results should be considered preliminary. The operational measures of effectiveness (MOEs) included ATM utilization rate, average travel time, travel time reliability, and total travel time delay. The safety MOEs included crash rates by type and severity and incident frequency. These MOEs were analyzed using INRIX travel time data, limited traffic volume point sensor data, police crash reports, and iPeMS traffic incident data. Segment-level analysis was performed to determine the segments that benefitted the most from ATM implementation. From this segment-level analysis, it was determined that HSR was the ATM component that led to most of the improvements on I-66.

The results of the study indicate that the ATM produced positive operational and safety benefits across multiple MOEs. The ATM generally had limited operational and safety impacts during the weekday peak periods and some impacts during the midday and off-peak weekday periods. Average weekday travel times during the midday period in the off-peak direction typically improved by 2% to 6%. However, weekday peak period travel times and travel time reliability in the peak direction continued to degrade after ATM installation. This was not surprising given that HSR was already in use during the weekday peak periods before ATM activation and there has been a historic trend of increased travel times on the corridor. There were large operational benefits on weekends, with average travel times and travel time reliability improving by approximately 10% during the weekend peak periods. The weekend improvements were most likely due to the activation of HSR, which had not been active during weekends before ATM implementation, so the additional capacity served to alleviate congestion after activation. The safety analysis showed promising results for weekends, but no solid conclusions could be formed because of the limited data available for the safety analysis.

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