Commuters using I-66 yesterday may have gotten a rude post-vacation surprise, as Virginia state troopers set up checkpoints during morning and evening rush hours to step up enforcement of the highway's carpool regulations.

State police launched a crackdown on the highway yesterday with stationary road checks at several locations inside the Capital Beltway between 7 and 9 a.m. and 4 and 6 p.m., the times when HOV-3 rules requiring at least three occupants per vehicle apply, according to Sgt. D.M. Smith.

Although the total number of motorists stopped was not available last night, Smith said that at one checkpoint, on I-66 at Rte. 7 during the evening rush hour, troopers issued 33 summonses to drivers of cars carrying fewer than three people.

Smith said police plan to continue daily morning and evening checkpoints. The stepped-up enforcement, he said, is being undertaken because many motorists were simply ignoring the rules.

"In the past, we've been short in manpower . . . . We're planning to increase our checking details on I-66 now that we have the manpower."

In the past, Smith said, troopers set up three or four checkpoints a week, often stopping more than 200 motorists. During one checkpoint he helped supervise several weeks ago, troopers issued 88 summonses in two hours, he said.

Smith said the four to eight troopers who supervise each checkpoint do not stop every car. "We just try to get traffic to slow down," he said. "If we note a vehicle that has less than three persons, we pull that vehicle over."

Motorists who are stopped receive summonses for failing to obey a highway sign, an offense that may cost them up to $45 and three points toward suspension of their driver's licenses.