WASHINGTON — Drivers take whatever information they can get to plan their commute and beat traffic. Many rely on the electronic signs over the highway or freeway that say how long it will take to get to the next interchange or next city.
After seeing those signs along I-95 between Baltimore and Washington, one viewer asked us how those signs get their information.
QUESTION
Do highways and freeways track drivers to come up with travel time estimates?
SOURCES
ANSWER
Yes, highways and freeways use data provided by cars and drivers to estimate travel times.
WHAT WE FOUND
Maryland and Virginia have dozens of signs showing drivers how long it will take them to get to the next major interchange or how much the next stretch of toll road will cost.
It turns out, drivers provide that information.
In emailed statements, spokespersons for the Virginia Department of Transportation and Maryland State Highway Administration said the signs in each state use vehicle probe data.
According to the Federal Highway Administration, vehicle probe data comes from monitoring the real-time position of vehicles over a stretch of road. The highways have sensors near the sign, which marks the beginning of the stretch of road being measured. The data collected by those sensors may come from a car’s navigation system; a toll tag; a transponder on a bus, taxi, or other fleet vehicle; or phone apps such as Waze and Google Maps.
When the vehicle reaches the sensor at the end of the zone being measured, the travel time system calculates its speed. The outliers are removed so that the system can provide a realistic average travel time over the given distance.
The spokesperson for the Maryland State Highway Administration also said its system runs 24 hours a day and updates its times every four minutes. However, its signs only display the information when traffic reaches a certain level of congestion.