Tolls charged to solo drivers using MnPass lanes are based on traffic congestion and an algorithm that adjusts rates every three minutes — far less time than most rush-hour motorists spend in the express lanes.

That had Drive reader Jeff wondering: Can the price of a MnPass trip cost more than what is advertised on electronic signs if the rate goes up after a driver enters the lane?

The answer — with a couple caveats — is no. Once a driver enters a MnPass lane, the advertised rate is locked in for that segment of the trip, even if the rate changes during travel, said Brian Kary, director of traffic operations at the Minnesota Department of Transportation's Regional Traffic Management Center.

"If it went from 50 cents to $1, you pay 50 cents," he said. "We want to keep motorists happy."

Tag readers that deduct tolls as drivers pass by are spaced along the MnPass lanes on I-394, I-35W and I-35E. It's possible there could be a price adjustment in the short time it takes a vehicle to travel from a sign displaying the current toll to a tag reader, but that's a rare occurrence, said Sue Gergen, a MnPass spokeswoman. When it does happen, the system is smart enough to default to the lower price, she said.

The system notes the time a driver passes a tag reader and the toll in effect at that time, Kary said. When a driver reaches a second tag reader, the same process occurs. But the system also looks back to see what a driver was charged when first entering the lane, and what fee was in effect during the prior three-minute interval.

A driver entering the lane at 7:20 a.m., for example, could see a $1 toll but when passing another tag reader at 7:25 a.m. could see the fee went up to $1.50.

If the rate was lower during the first interval, the system defaults to the lower toll, Kary said.

"Once you are locked in, you are locked in," he said.

The western section of I-394 through Wayzata and Minnetonka is where there is the greatest distance between a sign and a reader, but it's also typically not congested, so a MnPass customer should be able to see the sign and pass the reader in the allotted time, Gergen said.

There are two caveats.

The MnPass lanes on I-394 are divided into two sections: the reversible lane between Hwy. 100 and downtown Minneapolis and Hwy. 100 west to its terminus in Wayzata. Those sections are tolled separately, and drivers could pay a different toll on each section, even if making one continuous trip.

Drivers who leave the MnPass lane and return later would be subject to the toll in place at the time of re-entry, Gergen said.

Of course, there could be a mistake. Customers with questions about their MnPass statement or fees can always contact MnPass customer service to confirm, Gergen said.

Tolls on holiday

The Drive noticed collection signs on I-35W on Memorial Day were showing a trip from the Crosstown to downtown Minneapolis cost 75 cents and wondered if somebody didn't realize it was a holiday and forgot to turn them off.

Not the case, Kary said.

MnPass lanes are in effect from 6 to 10 a.m. and from 3 to 7 p.m. weekdays, with the reversible lane on I-394 tolled 24 hours a day. While MnPass lanes are always free for carpools, buses and motorcycles, solo drivers have to pay.

"There is no exclusion for holidays," Kary said. "We do continue to restrict and toll the MnPass lanes on holidays."

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