Frustrated D.C. drivers took to social media to document their commuting woes on Jan. 20. Light snow fell and caused traffic jams and minor crashes on busy, slick roads. (Jenny Starrs,Victoria Walker/The Washington Post)

If Wednesday night was the Washington area’s dress rehearsal for this weekend’s winter storm, then we need a lot of practice — and fast.

A light snow began to make area roads slick about 7 p.m. and caused a commuter nightmare that must have summoned the memory of a snowstorm in 2011 that trapped commuters for up to 13 hours. Drivers said the roads apparently had not been treated.

With about an inch of snow in many spots, drivers in the District and on major suburban thoroughfares crept along.

Robert Fletcher, 57, left his Farragut Square law office before 7 p.m. and headed toward a 30-minute, 12-mile commute to his Falls Church home. More than four hours later, he was calling his wife from behind the wheel of his Infinity, hopelessly mired in a miles-long backup on Interstate 66 just west of Rosslyn, inching less than a half-mile in four hours.

“This is an unbelievable situation. It’s just a dangerous situation, and the authorities are doing absolutely nothing. I just don’t understand,” Fletcher said in a telephone interview.

Snow falls as pedestrians and commuters make their way down L Street NW in Washington. (Robert Miller/The Washington Post)

Also in Virginia, major delays continued near midnight on interstates, including I-395, I-66 and I-95. Traffic backed up for more than a mile on approaches to the Woodrow Wilson Bridge from Virginia to Maryland just before midnight, as weary drivers saw no end in sight.

D.C. Mayor Muriel E. Bowser (D) appeared to miss the potential hazards of a slight amount of snow.

At a midday news conference Wednesday, she focused on the impending weekend storm and not once mentioned the possibility of snow affecting the city earlier for the evening commute.

Speaking from her city-issued SUV while driving up Georgia Avenue after 10 p.m., Bowser called into Fox 5 News and said the entire region was affected and that the precursor to Friday had brought “more snow than was forecast.”

Bowser said that city crews had been pretreating arterial roads since 4 p.m. A spokesman for her office said there were more than 70 accidents in the District on Wednesday evening.

Asked if Wednesday night’s gridlock should give residents pause about the city’s preparedness for a larger storm, the mayor told Fox 5 that the city would take precautions to get motorists off the road before the storm.

“We, of course, will put safety first,” she said.

A snowstorm headed toward Washington, D.C, and the Mid-Atlantic is expected to last 36 hours between Friday and Sunday. Capital Weather Gang's Angela Fritz has your forecast and snow accumulation predictions. (Ashleigh Joplin/The Washington Post)

A Maryland State Highway Administration spokeswoman said the roads were not pretreated because the forecast was calling for no more than a squall.

Spokeswoman Kellie Boulware said that as the snowfall continued, the highway agency pulled in additional crews, which were to work through the night to treat slick roads in preparation for the morning rush.

In Virginia, state transportation officials did not pretreat roads because forecasts called for temperatures so low that the treatment might freeze on roads, making them more hazardous. “It only takes a little bit of ice to create a very serious situation,” said Jennifer McCord, a spokeswoman.

In Arlington, the county’s Department of Environmental services said they began pretreating roads with brine early Wednesday afternoon, in preparation for the week’s forecast.

“We’re currently fully mobilized, and will be through the night, treating with salt on our primary, secondary and school routes,” said spokeswoman Jessica Baxter.

Michael Czin, a spokesman for Bowser, said that the District’s 911 and 311 phone lines were burdened Wednesday night by an unusually high number of calls, mostly about snow-related fender benders.

Some callers had difficulty connecting to 911. Czin encouraged residents not to call unless it was a true emergency and to use the 311 cellphone app instead.

“Top recommendation: If you don’t have to drive, stay home,” said Mark Brady, a Prince George’s County fire department spokesman.

In Montgomery County, rescue crews responded to dozens of accidents, and officials placed the county communications center on “code red” status to deal with the call volume.

“We are quite busy, in particular on the Beltway, Route 29 and I-270, said Pete Piringer, a spokesman for the county Fire and Rescue Service. “We had a rash of wrecks in the Burtonsville and White Oak areas.”

Piringer also said Montgomery fire crews found a man unconscious inside a Gaithersburg townhouse, suffering from carbon monoxide poisoning caused by a generator. The man was taken to a hospital with potentially life-threatening injuries.

Fairfax County police had to deal with more than 50 crashes, which did not include calls for stuck vehicles and other hazards.

Even President Obama’s motorcade was affected, making its way from Joint Base Andrews at 7:26 p.m. and through suburban Maryland and the District. The vehicles stopped at most stoplights and eased their way through the slow-moving traffic, often employing sirens and flashing lines.

After nearly an hour, the vehicles, slipping and skidding, started making more aggressive use of their sirens and stoplight privileges. The ride ended at the White House at approximately 8:40 p.m.

Fairfax officials reported sheets of ice in spots throughout the county, and police responded to accidents and poor conditions on major roads, including I-495 near Route 50 and Van Dorn Street; I-95 near the Fairfax County Parkway; and Braddock Road at Clifton Road.

In the District, police responded to several incidents and situations that backed up traffic, including a hit-and-run on Alabama Avenue SE, disabled vehicles on the 14th Street bridge and icy conditions that caused police to shut down the Third Street Tunnel’s southbound ramp. Police called for a salt truck to treat the road surface on the bridge.

“I can’t even keep track of all of them,” a dispatcher said of all the traffic tie-ups.

Aaron Davis, Mary Pat Flaherty and Julie Zauzmer contributed to this report.