In Transit: How tollway travel times are calculated
It's 17 minutes from Arlington Heights to Route 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 International Airport and Barrington Road that display real-time road information.
The Smart Corridor offers more bells and whistles than existing digital signs on the Tri-State, Reagan Memorial and Veterans Memorial tollways, but the methods used to calculate travel 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.
I've found the posted commute times on I-355 to be pretty accurate, although off by three to five minutes sometimes. But I-90 regular and Daily Herald Director of Photography Jeff Knox calls the Jane Addams prognostications bang-on.
That's likely because there are more devices on the rebuilt I-90, Mathura said. "The more data, the more accurate the time is."
But how does the legion of tollway 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 technology 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. At the same time, the Traffic Operations Center will expand from running 24 hours a day weekdays to 24/7.
Matharu, who commutes from home in Evanston to tollway headquarters in Downers Grove, relies on Tri-State travel times and says they reduce stress for drivers.
"If they know they'll get there in 12 minutes (for example), it puts them at ease."
You should know
As cleanup and drying out continues amid flooding across Lake County, Pace is advising riders that some services such as paratransit are using detours and experiencing delays. If you will be traveling in an area still impacted by flooding, contact customer relations at (847) 364-7223, option 3, for information.
Dean Worthem of Hanover Park doesn't blame faulty tank cars following a recent CN derailment that spilled crude oil in Plainfield. "I think the main reason for the derailment is the tracks," Worthem said. "It's not the train cars at all. Sure, let's make the cars bulletproof, but the problem is yet to be fixed. I truly believe that railroads need better and more thorough inspections to stop these accidents before they happen.
"And to think Illinois wants a high speed rail line?! Thanks I'll pass."
Work on safety improvements including extension of a barrier wall to the Tri-State (I-94) at Grand Avenue in Gurnee begins this week. Expect closure of the ramp connecting eastbound Grand Avenue to westbound I-94.