Police plan a one-day campaign Thursday against drivers who violate HOV rules in Virginia and Maryland.

HOV enforcement Virginia State Police pull over drivers at an entrance ramp to Interstate 66 during an HOV enforcement campaign in 2010. (Gerald Martineau/For The Washington Post)

In Virginia, police will target Interstates 66, 95 and 395, as well as the Dulles Toll Road. Many agencies are involved: Virginia State Police, Metropolitan Washington Airports Authority Police, and police from Arlington, Fairfax and Prince William counties.  Maryland State Police plan to target I-270.

The stepped-up effort against violators will occur during both morning and evening rush hours, the time periods when the HOV rules are in effect on those highways.

Enforcing the rules presents difficulties for both officers and commuters. Stopping motorists to issue tickets usually means the police are walking highway shoulders and ramps, which leaves them vulnerable in heavy traffic. And such enforcement operations always draw attention from other drivers, slowing down travel when traffic volumes are at their highest.

The police agencies announcing the campaign said they would be monitoring the traffic conditions and adjusting their efforts to ease any additional congestion.

They’ve done this before. During last year’s regional campaign, police said, they recorded 485 violations.

If you’re out on the highways Thursday, it’s a good idea to remember that police also enforce their states’ “Move Over” laws, which require drivers to either move to an adjacent lane or slow down when they see a stopped police or emergency vehicle with lights flashing.

One question that Virginia drivers often ask about the HOV rules has to do with the timing issue on the I-95/395 lanes, since those lanes are separated from the rest of traffic. That system is HOV3 (three persons in a vehicle) from 6 to 9 a.m. and 3:30 to 6 p.m. weekdays. Drivers who don’t meet the rules are permitted to use the lanes at other times, as long as they’re going in the right direction. So solo drivers often ask if they’ll be okay if they get into the lanes just before the rules take effect.

The answer is no. If a driver who doesn’t meet the rules is in those lanes at any time during the HOV hours, then the driver is in violation of the rules.

Another frequently asked question is whether being pregnant counts in meeting the HOV2 rules on other highways. It does not. But a child of any age does count toward the total in the car. A passenger does not need to be of driving age to qualify in the HOV system.