Dear Dr. Gridlock:

I was about to purchase the new 2012 Toyota Prius Plug-in.

However, to my surprise, the dealer told me the car will not qualify for high-occupancy vehicle access on Interstates 66 and 395.

Apparently, the same applies for all the new electric vehicles!

What is the incentive to purchase those vehicles if less-efficient hybrids have HOV access but not the new electric cars.

— Pierre Rahal, Arlington

Virginia’s rules for who’s legal in the HOV lanes are a mess — and they keep changing. No wonder drivers are confused.

I said on last Sunday’s Commuter page that the answer to one of springtime’s most frequently asked questions is that, yes, the Virginia General Assembly and the governor have once again decided that hybrids can continue using the lanes created for carpoolers, even if they have too few occupants to meet carpool requirements.

But I spared you the details.

Now you’re in for it.

Virginia’s hybrid exemption started off as a well-intentioned effort to encourage the purchase of vehicles that would be better for the environment. But commuters who went to the trouble of carpooling saw that the HOV lanes were becoming more congested because of solo drivers in hybrids. This cut the incentive to carpool.

The supposedly temporary hybrid exemption kept getting extended by the General Assembly, but restrictions were gradually imposed. Those restrictions are a bit different depending on which HOV lanes a hybrid is in.

This is how the Virginia Department of Transportation states the rules for the lanes in Northern Virginia:

On I-66, only hybrid vehicles with clean-fuel plates issued before July 1, 2011, are permitted to use the HOV lanes during rush hours. Police will ticket any hybrid vehicle that does not have a clean-fuel plate issued before that date.

On I-95 and I-395, only hybrids with clean-fuel plates issued before July 1, 2006, are permitted to use the I-95/395 HOV lanes during rush hours. Police will ticket any hybrid vehicle that does not have a clean-fuel plate issued before that date.

On the Dulles Toll Road, the only requirement is that the hybrid vehicle have a clean-fuel plate. But only certain types of hybrids are eligible for clean-fuel plates. They’re listed on the Virginia Department of Motor Vehicles Web site, And by the way, you D.C. and Maryland residents who keep asking, you’re out of luck entirely. The hybrid exemption applies only to drivers with the proper Virginia plates.

You know whom I feel sorry for? The police who have to enforce all these rules. Once they get past the cheaters who are putting wigs on dummies so they look like passengers, then they have to sort through the hybrid license plates.

The Prius Plug-in that Rahal checked out is an advanced type of hybrid that allows drivers to go more miles on electric power before resorting to gasoline, according to a review by The Washington Post’s Warren Brown. And the plug-in is listed among the 2012 vehicles that would qualify for Virginia clean-fuel plates — just not the kind that would let a new buyer qualify for the I-66 and I-95/395 exemption.

So is it worth buying? Here’s what Brown said in his review: “Yes, it is — in the manner that cleaner air and moving toward a more stable and, eventually, more affordable energy future are worth it.”

Cleaner air? That’s it? He doesn’t say anything about paying a premium so you can drive faster than the people in the regular lanes on the big commuter highways.

Come to think of it, that sounds like the idea behind the high-occupancy toll lanes, scheduled to replace the HOV lanes on I-95.

But even with the HOT lanes, it’s bad news for the hybrid drivers. No more exemption for any of them. They’ll all have to pay the toll unless they carpool.

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or e-mail