JUDGING FROM the number of untended government and business phones from Thursday on, the advance motorcades of holiday weekenders were off and rolling early, with still more merging into the flow yesterday. As the locals depart (with hands-free cell phones, we trust), the tourists arrive to soak in the patriotic glories of their nation's capital. In all, AAA Mid-Atlantic estimates, more than half a million residents will have left here by car, making this the busiest summer travel weekend in a decade. One unpleasant tradition: It also is one of the deadliest times of the year on the roads. Speeders and drinkers come out of nowhere.

They may not care all that much, but they should know that the odds of their getting nabbed are likely to be better than ever this year. In particular, travelers in Virginia will find authorities armed with 25 new laws aimed at stopping drinking and driving, making the state one of the toughest anywhere. Most of the new laws zero in on repeat offenders and "super drunks" -- drivers found to be the most heavily loaded. They will be in for harsh punishment, including longer mandatory sentences. The legislative crackdown, which took effect Thursday, was dreadfully long in coming, but this year the General Assembly reacted forcefully after alcohol-related deaths rose in recent years. As reported by The Post's Karin Brulliard, 375 people died in drunken driving accidents in the state in 2002 -- 18 more than were murdered that year in Virginia.

There, as well as in all other directions from the Washington area, law enforcement authorities again are out in full force with radar, speed cameras, planes, helicopters, unmarked cars and sobriety checkpoints. Even with all this in place -- and with everyone in seat belts or properly installed child safety seats -- some drivers will have had another kind of belt for the road and others will be bobbing and weaving at terrifying speeds. They bear watching.