Dear Dr. Gridlock:

Can you shed some light on Virginia’s recent decision to start charging a monthly fee for the E-ZPass transponders? I’ve had mine for years and was charged a deposit for it. Does this mean not only that Virginia will keep the deposit until I return it, but also that I will be charged monthly?

This seems counterintuitive. The transponders are supposed to cut down on operation costs, because there isn’t a person collecting the funds at each toll booth. It might make more sense for toll collectors to charge more for people who don’t have a transponder.

— Katrina Martin, Alexandria

“We haven’t done anything yet,” Virginia Transportation Secretary Sean T. Connaughton told me last week. The Virginia Department of Transportation had announced a few days earlier that it was “considering a new fee structure to provide customer support for the increasing number of accounts, transponders and electronic toll collections.” Among the items being considered: a $1 a month maintenance fee on Virginia E-ZPass accounts.

VDOT promised there would be more chances for more public comment before a decision is made.

Connaughton echoed that, but he did note that the state expects to take on hundreds of thousands of new E-ZPass accounts this year for drivers who want to use tunnels in the Hampton Roads area and the 495 Express Lanes on the Capital Beltway.

I understand that the agencies that issue the transponders and maintain the accounts incur significant back-office costs that are either going to be covered through taxes, tolls or monthly charges on the users. I said that to Marylanders several years ago when the Maryland Transportation Authority began charging $1.50 a month for accounts.

VDOT said the annual operating cost of the E-ZPass customer service center is $10 million, and that’s just part of the cost for running the system of transponders and accounts.

This is what would really bother me: If Virginia’s slugs — the commuters who for years have gone to the trouble of carpooling for the trip along Interstate 95 — have to start paying to do the right thing.

That would happen if they have to pay a monthly account fee, or any other fee, to use what are now high-occupancy vehicle lanes on I-95 and will become high-occupancy toll (HOT) lanes in 2015.

It’s one thing to require carpoolers who want to use the Beltway express lanes for free to get transponders and establish fee-supported accounts. Those lanes, scheduled to open at the end of the year, will be brand new lanes.

But the I-95 carpool lanes are long-established, and very successful, thanks to the slugs. They’ve long feared the impact of converting those lanes to HOT lanes. Specifically, they feared that they would be charged to carpool.

It’s tough enough to get people in the D.C. region to share rides and thereby reduce the number of cars jamming the highways. It’s not fair to start charging them — even $1 a month — to continue helping us with the congestion problem.

Connaughton, former chairman of the board of supervisors in the slugging homeland of Prince William County, didn’t commit to any particular option. He did make the case about the operating costs the state anticipates, and he did cite the various ways HOT lanes would help carpoolers.

Their daily rides would be free. Hybrid vehicles that have an exemption from carpool rules in the HOV lanes would be ousted from the HOT lanes. And the cheaters who may account for 40 percent of the HOV lanes traffic would stand a better chance of getting caught in the HOT lane system.

But the commonwealth still ought to be able to come up with a creative solution that exempts the slugs from any fees.