Quandary: How CDOT calculates travel times | SummitDaily.com

Quandary: How CDOT calculates travel times

This 30-second exposure photograph shows traffic at the Silverthorne exchange. Road signs along Interstate 70 let drivers know how long of delays to expect, as well as other useful information.
Bill Linfield / Special to the Weekender


Quandary, the old and wise mountain goat, has been around Summit County for ages, and has the answers to all questions about life, love and laws in the High Country. Have a question for Quandary? Email your queries about Summit and the High Country to Quandary@summitdaily.com.

Dear Quandary,

How are the travel times calculated for signs on I-70?

Isn’t it handy when you get on Interstate 70 down in Denver, see the bright yellow lights above you reading, “Eisenhower Tunnel 3 hr. 5 min,” and you can turn back around and grab some lunch before you even get stuck in those long traffic lines? But alas, nothing in life is that simple. Without diving too deep, you soon realize this is one of those times when we trade privacy for convenience. It’s like socialism on wheels. Bob in the Odyssey gets his tag read all the way up the mountain for Suzie in the Subaru’s convenience at the bottom of the hill. As long as you know that’s what you’re getting into, it all works fine.

In order to calculate travel times, the Colorado Department of Transportation reads toll tags and looks at sidefire radar and TTI, or Travel Time Indicators, to figure out how long a trip will take, and where the problems occur. It’s not quite as simple as a one-to-one ratio though — for much of this they are actually reading the speed in front of the radar, not necessarily the vehicle itself. CDOT doesn’t just watch poor Bob’s struggles and relay his plight to you. Instead, the data is collected from several vehicles and transmitted back to CDOT where they then use an algorithm to determine speeds and travel times. Once the data is run through the computer, the system will then pop up with its master calculation on signs all along the road. This whole process happens every two minutes, too. This means that soon after a road rage incident turns into a 20-car pileup, drivers all along the route will know something is wrong up ahead. In circumstances of large crashes or road closures, that information will often be displayed on the sign as well. In that case, there are three little words that make gas tanks cry across the country and let you know it’s time to turn around: “Alternate routes advised.”

Beyond displaying travel times and ominous warnings, the road signs also allow CDOT to communicate statistics and driving tips to road warriors. Think of them like a grandma who grows increasingly more concerned with your life choices as you go along. If it helps get the message across feel free to read it with your name. Something like, “You know, Richard, the left lane is for passing only” soon escalates into panic mode with, “Richard, please! Move over and slow down for emergency personnel.” Finally, at the point where your imaginary grandmother would be stomping on the imaginary brake, you might read something like, “537! There have been 537 traffic fatalities this year.” The implication being you’re No. 538 if you don’t shape up.

Regardless of which family member you think these signs represent, big brother or nagging grandmother, know that the intent is to be helpful. If you already are an expert driver, feel free to ignore the signs, but be forewarned, no amount of skill is going to get you out of a three-hour wait at the tunnel.

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