The Phase II Evaluation Report detailed the ATM strategies implemented and the corresponding safety evaluation.
This Phase II project evaluated the performance of an Active Traffic Management System (ATM) system installed on I-66 in Northern Virginia. An operational analysis was conducted from October 2015 through November 2017 and a safety analysis was conducted from October 2015 through December 2016.
In early 2013, construction began on a Virginia Department of Transportation (VDOT) project to install an ATM system on I-66 from US 29 in Centreville to the Capital Beltway. Construction was completed in September 2015 and spanned approximately 12.4 miles. The primary ATM strategies implemented on I-66 included:
- Variable Speed Limits (VSL): On I-66, the normal posted speed limit is 55 mi/h, but the VSL system can post speeds between 35 mi/h and 50 mi/h above each lane depending on traffic conditions.
- Hard Shoulder Running (HSR): The I-66 HSR system dynamically opened or closed the shoulder lanes depending on roadway conditions.
- Lane Use Control Signals (LUCS): For incident and work zone management, overhead gantries were deployed with LUCS to alert drivers to lane blockages.
A segment-level analysis was performed to determine the segments that had benefitted the most from the implementation of the ATM system.
The safety evaluation showed 6 percent, 10 percent, and 11 percent reductions in total (all severity), multiple-vehicle (all severity), and rear-end (all severity) crashes, respectively. Further analysis again demonstrated segments with HSR saw the largest safety improvements.
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. Most of these improvements occurred on HSR segments.