Virginia Gov. Robert F. Mc­Don­nell (R) has signed the now-traditional, one-year extension of the temporary law allowing solo drivers to use the lanes meant for carpoolers as long as they have the proper clean fuel license plates.

But there is an important difference this year: Drivers who want to take advantage of this legal end-run around the carpooling requirement to drive on Interstate 66 High Occupancy Vehicle lanes need to buy their hybrids and get the clean fuel tags by June 30. After that, they can still buy hybrids, but they’ll risk getting a ticket if they drive in the I-66 HOV lanes. Police look for the proper tags, not for the type of vehicle.

This change in the I-66 rules that grandfathers in clean fuel license plates issued before a certain date and then cuts off newcomers is similar to a provision that took effect in 2006 regarding hybrid driving on the I-95/395 HOV lanes. That was a concession to the concerns of carpoolers and the Virginia Department of Transportation that hybrids with solo drivers were on their way to clogging the HOV lanes, diminishing the incentive to carpool for a faster trip.

If you’re planning a purchase, be sure to read the rules for clean fuel tags on the Virginia Department of Motor Vehicles Web site. Not all hybrids qualify for the tags. The state’s annual fee for clean-fuel plates is $25, and $15 goes to the Virginia State Police HOV enforcement fund.