TACOMA — Washington state transportation officials plan to use Bluetooth devices to track traffic congestion near Joint Base Lewis McChord over the next few weeks.

The Department of Transportation is going to watch the signals these devices emit as part of its traffic study, The News Tribune reported. They assure private citizens that transportation officials won’t be listening in on their phone calls or track who is making phone calls.

“We cannot track people or hear conversations, nor do we want to. All we know is the signal,” said Jon Pascal, principal at Transpo Group, the Kirkland-based company deploying the Bluetooth readers. “We don’t know where it’s coming from; we don’t know if it’s a car or a phone. There’s no way to track it.”

Cell phones aren’t the only devices that transit the Bluetooth signals. Some cars report tire pressure and other maintenance needs through the same network.

Forty-seven readers will be installed from just north of state Route 512 in Tacoma to Lacey and from state Route 507 in Yelm to Steilacoom. Time, date and location stamps will be recorded. The data will be combined with other traffic studies to determine how people use the regularly congested stretch of interstate.

Traffic officials assume the bottlenecks in the Lewis-McChord area are from people who use I-5 to get to different points on base, but officials don’t have data to support those assumptions, said Bill Elliott, Olympic region coordinator for the state DOT.

If the study shows that’s the case, it could prompt a recommendation to add arterial routes on base to reduce the number of drivers using the freeway, Elliott said.

This study will help the department learn where people are coming from and where they’re going, he said.

“Doing it manually with people with cameras would have been completely impractical,” Elliott said.

Typically the department uses a person to photograph license plates for these types of studies. With such a large area under review, that was too labor-intensive.

The department knows not everyone has a Bluetooth device and expects the study will capture roughly one-quarter of vehicles using the corridor daily, but that is statistically adequate.