“I’m also just plain curious,” she said.
Washington State Department of Transportation spokeswoman Tamara Greenwell said the agency uses radar sensors or sensors in the pavement to measure the speed of passing vehicles, and density of vehicles on the roadway.
The sensors in the pavement — inductive loops — work like metal detectors, Greenwell said. When a metal object, such as a vehicle, passes over or stops within the sensor’s detection area, it trips the sensor.
Greenwell said these units often need ongoing maintenance, and have to be replaced whenever a road is repaved, and that fixing them requires cutting into the pavement. She said WSDOT is trying to use more radar sensors where feasible.
The sensors feed their data into a computer program that calculates an estimated travel time between two points, and that information is displayed on the readouts. Oregon and Washington share traffic data, so drivers are seeing estimated times calculated in the same way whichever state they’re in.
The agency placed the signs at key spots, so drivers could have time to change their route if needed. The signs in Vancouver were installed in fall 2015.
Kootstra’s husband wasn’t necessarily that far off. Mapping applications such as Waze and Google Maps use, in part, location data shared from users’ smartphones to calculate traffic volume and travel times. They also use information from public transportation agencies.