The Drive reported two weeks ago that scores of commuters were still waiting for their MnPass transponders because the Minnesota Department of Transportation was a few weeks behind in filling orders. MnDOT now has caught up on the backlog.

The column generated a lot of discussion about the MnPASS program, through which solo drivers pay to use lanes reserved for buses, motorcycles and carpools.

Several people asked whether they could use their MnPASS transponder in other states, while others wanted to know if they were being charged for using the pay lanes on days when they carry passengers and qualify as a high-occupancy vehicle.

MnPASS is not compatible with other systems such as Illinois' I-PASS or the E-ZPass system that is used in 15 states, primarily east of the Mississippi River. Those states have millions of users, collect fees on their large system of toll roads, and share technology. They also have agreements on transferring funds between states.

MnPASS is much smaller, with just 20,000 customers. To join with the other states, Minnesota would have to install a separate set of antenna readers to the MnPASS lanes or make a major investment in technology to make the system compatible, said Brian Kary, a MnDOT freeway operations engineer.

"The costs associated with that would be easily in the six figures, if not over $1 million due to the infrastructure replacement," Kary said. "We need to ensure that it makes good business sense and is of value to enough of our customers to justify the expense. For [the other states] it's easier to justify the costs."

Kary said the number of MnPASS customers is much lower because Minnesota does not have toll roads.

It's possible MnPASS will be compatible with systems in other states in the future. Last summer, Congress passed a federal transportation spending bill that requires tolling systems be interoperable by October 2016. Kary said the tolling industry is developing technologies that are less proprietary and more compatible. By then, the metro's third MnPASS lane -- on Interstate 35E from the Cayuga Bridge to Hwy. 36 through St. Paul and Maplewood -- will be open and presumably will grow the customer base.

"We are still exploring what it would take to meet this goal of interoperabilty," Kary said. "Hopefully, changes in technology will make it easier and more cost effective."

As for the carpool question, motorists pay 25 cents to $8 per trip to use MnPASS lanes, but they don't have to pay on days they qualify as a carpool.

The transponder sits in a clip that is affixed to a driver's windshield. When attached to the clip, the transponder is on and ready for use. On days when a driver qualifies as a carpool, meaning the vehicle is carrying two or more people, the transponder can be removed from the clip and the transponder is turned off. No tolls are collected, Kary said.

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