A recent radio campaign marketing MnPASS lanes on Interstates 35W and 394 was so successful that in the past month more than 800 people ordered a transponder and had money withdrawn from their bank accounts for the right to drive  in the lanes reserved for buses, motorcycles and carpools.

It also created a problem. The sudden surge wiped out the supply of transponders.

Colin MacMillan has been waiting seven weeks for a transponder. Delays happen, he understands. But more irksome than sitting in traffic snarls as motorists with transponders zip by him in the High Occupancy Vehicle lanes is that he's heard nary a word from the Minnesota Department of Transportation (MnDOT) as to when he will get his.

"They didn't tell me that they don't have them, that they are coming or that I can expect it by a certain date," the Prior Lake resident told the Drive. "I didn't get an e-mail. I had [to initiate] an online chat, and all I got was, 'Sorry, but we have no information to give you.'"

The Drive learned that a fresh supply of transponders arrived at MnDOT's Roseville headquarters last week and informed MacMillan that he should soon have his.

"That's more information than I got from MnDOT," he said.

MnDOT just wrapped up a monthlong promotion to increase the number of solo drivers who pay to use the HOV lanes. Typically, the agency sees about 500 signups each month, said Brian Kary, freeway operations engineer at MnDOT.

"Seeing that bump and increase was a good thing, but it caught us by surprise," he said.

Each transponder comes with a battery that powers the device that, in turn, communicates with the system that deducts the toll when drivers use the lanes. The battery is not easily replaced, and its five-year lifespan begins as soon as the manufacturer installs it.

"We don't want to order too many and have them go old on the shelf, and potentially give a customer a transponder with a dying battery," Kary said.

MnDOT replaces a transponder at no cost when the battery dies. But between the number of replacements and requests, MnDOT didn't have enough on hand. The agency had to order a batch from the lone manufacturer contracted to make them.

"We'll be tracking our inventory closer and be more conservative with new projections so we don't run out," Kary said. "We've already placed another order."

Currently, about 20,000 vehicle owners have transponders. About 12,000 motorists use the original MnPASS lane on 394, which opened in 2005 when the carpool lane was converted to a pay lane.

About 8,000 use the MnPASS lane on 35W from downtown Minneapolis to Burnsville, MnDOT said.

A new MnPASS lane is set to come online in 2015 on 35E from the Cayuga Bridge to Hwy. 36 through St. Paul and Maplewood.

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