HOW TOLLWAY TRAVEL TIMES ARE CALCULATED
It’s 17 minutes from Arlington Heights to Illinois 59 via the Jane Addams Tollway ( I- 90), the digital message board claims.
But is it 17 minutes for the driver who faithfully sticks to the speed limit and passes on the left? Or 17 minutes for the lead- foot, weaving in and out of traffic?
Posted travel times aren’t just pulled out of a hat, Illinois tollway Traffic Operations Manager Amarpal Matharu explained. They’re calculated with a complex mixture of algorithms calibrating vehicle volumes and speed.
Currently, the agency is testing out features on its “Smart Corridor,” a series of dynamic message boards between O’Hare Airport and Barrington Road that display real- time road information.
The Smart Corridor offers more bells and whistles than existing digital signs on the TriState, Reagan Memorial and Veterans Memorial tollways, but the methods used to calculate times are the same.
Traffic speeds and volumes are collected when vehicles pass through toll plazas, and by pavement sensors and detectors mounted on poles. The agency also uses technology to capture speed data from vehicles with Bluetooth. That information, officials stressed, is kept anonymous.
The data is transmitted back to the Tollway’s Traffic Operations Center, squirted through an algorithm and — ta- da! — displayed on message boards that are updated every three minutes or so.
But how does the legion of drivers whizzing by at speeds over 70 mph figure into it all?
“We cap our speeds,” Mathura said. Drivers “may be going at 70 or 80 miles per hour, but we cap speeds at 55 miles per hour. That’s why you may get there sooner than predicted.”
Interestingly, when speeds get below 20 mph, the tech- nology doesn’t work as well, he noted.
Crashes also can be problematic for travel times because of unknown factors such as secondary crashes and arrival of emergency crews.
How do the Tollway commute predictions compare to rivals such as Google Traffic?
“We have a lot more data than Google” on toll roads, Matharu said. But he acknowledged studies show similar results whether 20 percent or 60 percent of vehicles are captured.
The Smart Corridor, which will include indicators showing if lanes are open or closed and crash alerts, is expected to go live Sept. 5. — Marni Pyke