Travelers slowed to a crawl -- if they moved at all -- on Saturday as Maryland's worst snowstorm in years made driving treacherous, grounded airline flights and disrupted bus and train service throughout the region.

Only a smattering of motorists ventured onto snowy highways, as plows and salt trucks toiled through the day to keep them passable amid snowfall that intensified in the afternoon. State transportation officials said all major arterials remained open, but urged people to stay put for safety's sake.

A few airline flights made it out of Baltimore Washington International Thurgood Marshall Airport Saturday morning, but by 1:40 p.m. the facility closed, and more than 100 scheduled flights were canceled, officials said. One Jamaica-bound flight spent more than six hours stuck on the runway and again at the gate before it could de-board about 100 frustrated passengers.

Ground transportation was only a little more reliable. Greyhound halted inter-city bus service throughout the region, with cancellations extending down into the Southeast and north to Boston. Amtrak reported "no significant delays" of its trains between Washington and Boston, though some were running 30 to 60 minutes late and long-distance trains slipped two to three hours behind schedule, a spokeswoman reported.

Locally, transit service slogged on. Early in the afternoon, about 80 percent of Maryland Transit Administration buses were running, though they limited their routes to main thoroughfares because snow made side streets impassable. By evening, only about a third of the buses were still in operation.

Light rail trains were running 15 to 20 minutes behind schedule, a spokeswoman said, but the subway was unaffected by snow and running normally.