Traffic Signal Improvements on McKnight & Route 19

By Brian M. Sullivan in conjunction with Technology Advisory Committee (TAC).

Have you noticed that traffic on McKnight Road is flowing more smoothly and quickly?

Yes, right now many people are not driving because they are working from home due to COVID-19. Yet something deeper and more technologically advanced is also at play.

Long-term residents of the North Hills may have bad traffic memories from McKnight. This important conduit to and from work, shopping and fun even developed a catchy nickname as a result: "McNightmare." While anyone familiar with driving in places like Washington, DC or Los Angeles might chuckle at Pittsburghers' complaints about "bad traffic," high-volume traffic flow and clunky, uncoordinated old sensor and signaling technology was a consistently frustrating combination. Magnetic lane sensors helped prevent side traffic from waiting "forever" to make a left turn. But each of the many McKnight intersections made these decisions independently, guaranteeing multiple stops and starts for anyone driving from Route 19 to I-279.

An added dimension is that McKnight suffers from the road equivalent of multiple personality disorder. Morning and afternoon rush hours have high flow along its length. Late morning and early afternoon, people patronizing businesses, restaurants and malls drive stronger cross traffic. On a seasonal timescale, traffic during the holidays gets as many people as possible across and along McKnight to and from the malls, particularly Ross Park. Any sensor and signal timing settings optimized to accommodate one of these traffic flow personalities was wrong, and extremely frustrating, for the others. The resulting traffic design compromise was like a swan. Sure, a swan can walk, swim and fly, but it doesn't do any of them very well.

Enter a new approach. Over the past several years, intersections along McKnight and Route 19 have, one-by-one, been upgraded with a new type of sensor and signaling system. The system includes radar and video detectors for nearly 100% vehicle detection accuracy. Rhythm In-Sync artificial intelligence software ("AI") integrates these new sensors with each intersection's traffic light control switches. AI triggers the intersection's light timing to optimize traffic flow through the intersection considering current vehicles traveling through the intersection, and times vehicles wait at different crossing and turning positions. The AI considers time of day, week, and year. There are different time of day and weekday/weekend plans always running (along with a different timing plan by the Ross Park Mall during the Christmas season to help with the increases in traffic there).

The first signals to receive this upgrade were in 2013 along Route 19 in the Wexford Flats (covering its intersections from North Allegheny Senior High School up to the intersection with North Chapel Road). In 2015, a few more signals on Route 19 in Pine were upgraded, and finally in 2019, the signals at Shenot/Northgate and Warrendale Bayne Road in Marshall Township were upgraded.

On McKnight Road, upgrades to signals from Nelson Run Road north to Perrymont Road took place in 2017, and then the remaining signals (Duncan Avenue north to Pine Creek Road) were upgraded in 2018.

Each intersection benefits from this adaptive traffic flow. Multiple adjacent adaptive intersections enable "whole that is greater than the sum of its parts" performance. The intersections wirelessly talk to each other to coordinate their signal timing. The coordinated timing optimizes flow along the whole road, not just at each intersection. The timing creates windows of high-density lengthwise flow alternating with cross traffic. The pattern minimizes stops and starts while traveling the length of McKnight and lets waiting cross traffic and turns proceed at the first gap after a pulse of lengthwise traffic. The system has the effect of bunching cars driving up and down McKnight, then letting them drive at the speed limit.

While traffic flow has improved over the years, additional improvements continue to be made, and sometimes interruptions still occur. If a sensor fails, it might not be immediately obvious to PennDOT and the Town. The Town is investigating methods to improve real-time remote monitoring of key intersections, and investigating improvements that could be made at other intersections. Stay tuned.