An unusual toll rate of $8.07 during the peak commute Friday morning on I-405 left some drivers wondering what was up, because tolls customarily rise and fall in 25-cent increments.

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Drivers on  Interstate 405 saw an unusual toll rate of $8.07 in the peak commute Friday morning,  to enter the express toll lanes from Bothell to Bellevue.

That didn’t make sense, because tolls customarily rise and fall in 25-cent increments, totaling between 75 cents and $10 depending on traffic flows. Signs on the Highway 167 high-occupancy or toll (HOT) lanes also showed some 7’s.

It turns out the .07 was a default signal to alert engineers, after computer servers failed to transmit correct toll rates to the signs.

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The toll rates constantly change, based on real-time data from magnetic loops in the pavement that measure passing cars. If the information flow halts,  computer servers are programmed to show a rate that’s based on two years of historic data — in this case tolls typically are $8 just before 8 a.m.

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In other words, the toll signs were making an educated guess.

The problem was fixed at 10:25 a.m., reported Ethan Bergerson, spokesman for the Washington State Department of Transportation.

Sevens might also appear if a power outage momentarily disrupts a connection, he said. WSDOT has backup generators to sustain the toll system during an Eastside outage, he said.

“This is, honestly, the system working the way it’s supposed to,” said Bergerson.

He emphasized that drivers always are free to choose whether to enter a toll lane, regardless of the posted rate.  A greater hassle Friday morning was a crash that blocked the southbound toll lane of I-405 near Canyon Park, shortly before 8 a.m.

And yes, drivers will be billed the posted rate, including the extra 7 cents.