Overview
Interstate 17 connects the Phoenix metropolitan area to northern Arizona destinations, including Flagstaff and various recreational areas. Weekend and holiday travel creates significant congestion, with limited alternative routes exacerbating delays during incidents. The Arizona Department of Transportation developed an innovative flex lane system to address these challenges. The I-17 reversible lanes adapt capacity based on directional traffic patterns, providing operational flexibility and enhanced incident management capabilities. The flex lanes represent a cost-effective solution that dynamically matches infrastructure capacity to demand, serving northbound traffic during weekend departures and southbound traffic during returns.
Project Scope
The I-17 flex lane system spans eight miles from Black Canyon City to Sunset Point, consisting of two reversible lanes constructed adjacent to existing southbound lanes. These lanes carry traffic in one direction at a time, alternating between northbound and southbound based on demand. A total of 58 automated swinging gates (Versilis SwiftGate HSG-40CW) are deployed to control the two slip ramps located at both ends of those flex lanes. The gates are deployed or retracted based on the traffic pattern. Vehicle Arresting Barriers (VAB) have also been implemented to stop an errant vehicle from entering the flex lanes in the wrong direction. At each approach, three dynamic Open Close message signs provided by Versilis inform drivers of lane availability in real-time. All I-17 flex lanes ITS components (Open Close Signs, Gates and VABs) are controlled and monitored from ADOT’s Traffic Operations Center (TOC) through a number of Versilis Commanders, acting as sequencers and offering all the necessary logic and checkpoints for a safe and reliable operation.The flex lanes operate seven days a week, typically serving northbound traffic Monday through Saturday and southbound traffic on Sundays, with flexibility to adjust based on actual traffic conditions or emergencies. The I-17 flex lane facility is notable as one of the few reversible lane systems with slip ramps using two lanes rather than one. The facility is also equiped with cameras, providing TOC operators full camera coverage of the segment, especially useful during reversals.
