This evening, homeward bound commuters may encounter snowy highway ramps, but they won’t be as easy to see as earlier today. (Robert Thomson/The Washington Post)

The commuters who couldn’t take a snow day, like many government employees and schoolchidren, are heading home this evening on roads that were lightly traveled today, and that may be a mixed blessing.

On the one hand, they have some room to maneuver on streets and highways that are slick, slushy or snow-covered. On the other hand, the lack of traffic didn’t give them the benefit of all those tires that otherwise would have mashed up and moistened the slush that was salted earlier Tuesday.

Drivers leaving office centers in the middle of the D.C. region may encounter more snow and colder temperatures than what they saw at work. The trickiest travel may occur when they get to their own neighborhoods. Many streets still need to be plowed, as the snow continues to fall. Highway departments normally switch from sanding and salting to plowing once the snow has reached about two inches on neighborhood streets.

The Virginia Department of Transportation, which is responsible for clearing most roads in Northern Virginia, said that its crews and 4,000 pieces of equipment would continue plowing and treating surfaces in Fairfax, Loudoun, Prince William and Arlington counties while the snow was falling, then turn special attention on treating icy spots overnight as the temperature continued to fall.

Those frigid temperatures will be an important problem overnight and may well affect the morning commute. Salt and other chemicals used to treat roads become ineffective under 20 degrees, VDOT said. The snow and ice that was treated during the day will refreeze overnight. Travelers should be especially cautious on bridges, highway ramps and any other surfaces that are prone to freezing or were lightly traveled today.

High winds could blow that powdery snow back into roadways, where it will refreeze.

The Maryland State Highway Administration, which takes care of the numbered roads in the state, had similar concerns for this evening. “Our crews are seeing quite a few vehicles spinning out along the highways, with many near misses and some collisions,” Administrator Melinda B. Peters said in a statement. “It is best to let the plow trucks work and stay off the road.”

The number of traffic crashes increased as the day went on, and police sometimes closed highway lanes because of the accidents, slowing travel even more for thousands of motorists.

Metrorail reported relatively few problems, but at 4:30 p.m., Metro buses were restricted to their safer and sometimes shorter snow emergency routes.

The Capital Weather Gang is looking for the snow to end between 8 and 11 p.m., from southwest to northeast.