What is cut-through traffic and how does your phone help Alexandria track it?

At a public meeting last week on a proposed cut-through traffic mitigation plan, city staff answered a pretty fundamental but surprising question: what is cut-through traffic to Alexandria and how is it calculated?

The city is considering moving forward with the second phase of a pilot program that aims to cut down on cut-through traffic avoiding the city’s arterial lanes by driving through residential streets to access the highways. The pilots specifically target drivers cutting through Taylor Run to access Telegraph Road and I-495.

Phase 1 adjusted signal timing to prioritize traffic on the arterial roads and slow the lights that let traffic from Taylor Run out to Telegraph Road. City staff said Phase 1 was a success. Phase 2, meanwhile, will keep the signal timing changes but fully restrict access to the Telegraph Road ramp from West Taylor Run Parkway.

Hillary Orr, deputy director of transportation, said in a meeting last week that the city collects data from Bluetooth devices — like cellphones — in cars.

“We have access to a platform called StreetLight Data,” Orr said. “It pings off Bluetooth devices — people’s cellphones, Bluetooth sensors in cars. It’s all anonymous data and it’s all averaged. We look at averages over time. But we are able to do origin-destination evaluation.”

Orr said this means the city can traffic entering an area, like Taylor Run, from outside of that area and track them to see if they’re leaving by Telegraph Road moments later.

“The way we’ve done this study is looking at folks pinging outside of the study area, then pinging in neighborhood streets, then at the Telegraph Ramp,” Orr said. “Only those who drove through the area then left the area count. If you drive through and go home, you’re not counted as cut-through traffic.”

Orr also addressed other concerns about the project, like questions about whether or not Phase 2 should be delayed until Metro resumes its normal schedule. Metro is planning another shutdown from September to October for Alexandria. Orr said Metro ridership, however, has not nearly risen back up to pre-pandemic levels and the change in schedule is unlikely to substantially affect street traffic.

“What we’ve seen is rail ridership is not back up right now.” Orr said. “Metro rail ridership is about 30% of what it was pre-pandemic, so a lot of people are already driving. We want to see what happens in the more immediate future.  That’s why we wanted to start this sooner rather than later. Frankly, if more people are driving because the Metro is shut down, this should help the congestion and help Duke Street flow better.”

The meeting did get some concerns from nearby residents, though, who say they are concerned the program is only shuffling the cut-through traffic to other side streets.

“I’m really concerned with this pilot because it seems like we’re just going to shift the problem away from West Taylor and we’re not reducing cut through traffic,” said Matt Kaplan, a nearby resident. “It’s just going to be at Cambridge Road and Duke Street. That intersection is really bad today. I don’t think things are going to be pushed to Quaker, it’s going to be pushed there. It’s not designed for that today and we’re going to be adding more to it.”

Kaplan said Cambridge Road already suffers from speeding and poor visibility.

Orr said the first phase of the pilot saw cut-through traffic on Cambridge Road decrease by 60%.

“We know that when we change the signal timing from Phase 1, we shifted traffic to Quaker Lane,” Orr said. “Quaker was still faster even with that shift than all the other neighborhood streets. What we think is people are putting in Waze and Google Maps and it’s routing them on the fastest route. If we can make Quaker Lane the fastest route, that’s where they’ll want to go.”

If the city does move forward with Phase 2 of the project, the city’s website said that could begin as early as next month and run until March.