RICHMOND, Va. (AP) -- A winter storm that started as rain - meaning roads couldn't be pretreated - followed by an unusually heavy snowfall and plunging temperatures resulted in the stranding of hundreds of motorists along a stretch of one of the nation's biggest interstate highways, Virginia officials said, as they defended their response to the gridlock.

There were no reported deaths or injuries from the calamity on Interstate 95, but plenty of outrage from motorists, some of whom were stranded overnight Monday into Tuesday, posting pleas for help on social media.

“We all need to be clear that this was an incredibly unusual event,” Gov. Ralph Northam said at a news conference, adding that he could understand drivers' “frustration and fear.”

Problems began Monday morning, when a truck jackknifed on Interstate 95 between Richmond and Washington, triggering a swift chain reaction as other vehicles lost control, state police said.

They mounted throughout the day as snow fell at a rate of up to 2 inches an hour, said Marcie Parker, a Virginia Department of Transportation engineer leading the effort to clear the interstate.

“That was entirely too much for us to keep up with,” she told reporters. “Consequently, with the amount of traffic that we had on the interstate, the trucks and the cars couldn't make it up and down the hills because we had too much snow and ice out there.”

Lanes in both directions eventually became blocked across an approximately 40-mile stretch of I-95 north of Richmond. As hours passed and night fell, motorists posted messages on social media about running out of fuel, food and water.

Prime Inc. truck driver Emily Slaughter said she was driving from New Jersey to Georgia to deliver vegetables to a FedEx facility and became stranded for five hours on the southbound side of I-95. She said everything on the road was fine until she hit Virginia.

“All of a sudden you could no longer see lines. It got a little scary there,” she said.

Slaughter said she soon came to a stop and she found out about the disabled vehicles on the radio and over social media.

“People were saying, `we're running out of gas' or `our kids are hungry,”' she said.

Meera Rao and her husband, Raghavendra, were driving home from visiting their daughter in North Carolina when they got stuck Monday evening. They were only 100 feet past an exit but could not move for roughly 16 hours.

“Not one police (officer) came in the 16 hours we were stuck,” she said. “No one came. It was just shocking. Being in the most advanced country in the world, no one knew how to even clear one lane for all of us to get out of that mess?”

Northam defended his decision not to activate the Virginia National Guard or declare a state of emergency.

He said the issue facing state crews was not a lack of manpower but the difficulty of getting workers and equipment through the snow and ice to where they needed to be. And he said a state of emergency, which would typically be declared hours or days before an event to create extra flexibility in responding, would have done no good.

Up to 11 inches of snow fell in the area during Monday's blizzard, according to the National Weather Service, and state police had warned people to avoid driving unless absolutely necessary, especially as colder nighttime temperatures set in.

Because the storm began with rain, crews could not pretreat the roads because the salt or chemicals would have washed away, officials said. Some traffic cameras were also knocked out by power outages. And Parker said the position of the traffic backups in relation to the interstate's express lanes meant they were not of much use to clear the logjams.

Crews worked throughout the day to clear the roadway, and traffic spilled out onto secondary roads, causing additional delays.

It took until around 8:30 p.m. Tuesday for the Virginia Department of Transportation to reopen the interstate. Authorities had announced earlier in the evening that all stranded motorists had made it off the highway, and road crews then focused on removing the remaining abandoned vehicles and making sure the entire stretch was plowed.

Officials never provided an estimate of the number of vehicles that tied up in the jam. Photos showed they numbered in the hundreds, if not thousands.

The storm also left passengers on an Amtrak train stranded in Virginia. Amtrak's Crescent left New Orleans on Sunday on its way to New York and got stuck near Lynchburg on Monday morning, when downed trees blocked the tracks.

Passenger Sean Thornton told AP that Amtrak provided food, but toilets were overflowing and passengers were furious. Amtrak planned for the train to complete its trip once the tracks are clear.

Kelly Hannon, a spokeswoman for the transportation department, apologized to motorists for the I-95 logjam and said the department would take an “exhaustive look” at the incident.

Marvin Romero, who was driving home from a family vacation in South Florida with his daughters, ages 10 and 8, took a rather optimistic view of the situation, despite spending 20 hours and a long, anxious night in the car.

“To me, I see it as a once-in-a-lifetime experience. How many people can actually say that they stepped on I-95, or they slept on I-95?” he said. “It's hopefully a story that I can tell my grandkids one day.”