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A massive traffic pileup shut down part of the Pennsylvania Turnpike for several hours Friday, as an estimated 50 to 100 vehicles crashed, flipped or spun out amid the slushy roadway — another impact of Thursday’s monster storm.

The main wreck occurred around 8:20 a.m. ET on a 3- to 4-mile stretch of the eastbound lanes in Bucks County, north of Philadelphia, reported NBC Philadelphia. A snow-related speed restriction — forcing cars to go no more than 45 miles per hour — had just been lifted at 6 a.m.

“My heart was just like … oh my God. There’s no words to express it," motorist Maria Schoeler, who saw the wreckage, told NBC Philadelphia. "It’s pretty crazy. It’s something you don’t expect with this many vehicles. It’s pretty treacherous."

Twenty-four people were taken to local hospitals with one serious injury, although none life-threatening, officials said.

SUVs, big rigs and jackknifed tractor-trailers littered the highway. Traffic was beginning to move before Friday evening's commute, although there were still several cars and at least one tractor-trailer on the road.

The chain-reaction crash appears to be the result of a rampant winter storm that dumped a second batch of snow along the East Coast and promised a rough commute for millions Friday morning.

The storm pummeled states from Virginia to Vermont on Thursday, dumping as much as 28 inches of snow, canceling thousands of flights, and causing at least 21 deaths. Utility firms reported that about 424,000 customers still had no electricity early Friday morning.

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After a short reprieve, the snow ramped back up on Thursday night. While the second wave stopped around midnight in Washington, D.C., it was expected to continue until 6:30 a.m. ET in New York City and even later in Boston.

"In all these cities people are going to be waking up to snow-packed streets — it’s going to be a treacherous commute," said Michael Palmer, a forecaster at The Weather Channel. "In New York and D.C. the snow should have stopped by the time most people get up for work, but it will still be on the ground and not going anywhere in a hurry."

So far we're seeing a lot of flooding and icing. Stay off the roads if you can. Alternate side parking is suspended. Meter rules apply. - First 4 Traffic NY (@Traffic4NY) February 14, 2014

By 4 a.m. ET Friday, the second blow of this snowy double punch was already affecting transport.

More than 1,100 flights into or out of U.S. airports were canceled for the day and there were hundreds of delays, according to FlightAware. These came after more than 6,500 U.S. cancellations Thursday and were mostly distributed among the New York and Washington hubs, as well as airports in Boston, the Virginias and Carolinas.

New York-area commuter rail service Metro-North said it was running the equivalent of its Saturday service on Friday, which is about 40 percent of full capacity.

"Hundreds of employees are working through the night to clear snow from station staircases and outdoor platforms, but the additional snow accumulating overnight may present challenging conditions for customers during the morning commute," New York's Metropolitan Transportation Authority said in a statement late Thursday. "All customers are advised to use extreme caution, hold handrails and stay away from the platform edge for safety."

Thundersnow occurring in parts of NE Maryland, SE Pennsylvania and central NJ including Baltimore, Philadelphia, & Trenton. - The Weather Channel (@weatherchannel) February 14, 2014

The region was still reeling from Thursday's first dose of the storm, which stretched from Texas to New England. It also left snow on the ground in 49 of the 50 states and left half a million homes and businesses without power in Georgia and the Carolinas.

The Weather Channel's Palmer predicted some rural areas in South Carolina - the worst-affected state - would not be back on the electricity grid for three days due to thick ice which downed trees and power lines.

While the second punch of the system affecting the Northeast was expected to be over Canada's Maritimes by sunset, this second system from Ohio is expected to hit New England on Saturday and dump another five to eight inches of snow.

The Northeast & New England could deal with winter yet again this weekend. Here's what we know: http://t.co/4B6wKt5noo -The Weather Channel (@weatherchannel) February 14, 2014

Thursday's heaviest snow fell in Pilot, Va., which saw a 28.5 inches throughout the day, according to the National Weather Service.

Totals were more modest in metropolitan areas: New York City's Central Park saw 9 1/2 inches, Philadelphia International Airport got almost 10 inches, and Baltimore-Washington International Airport was buried under more than a foot.

The 18 deaths already blamed on the severe weather looked to have risen late Thursday after three men died while shovelling snow in Baltimore, The Baltimore Sun Reported.

The second wave, which hit early Friday, was far less severe, adding another 2 to 5 inches from D.C. to New York before it moves farther north.

Many schools across the region were closed for Friday as several states, including New York and New Jersey, declared states of emergency.

In Connecticut, Gov. Dannel Malloy declared a state of emergency due to a salt shortage, NBC Connecticut reported. The state only has enough salt for one storm, and with another possible snow dump on its way from a system coming in from the Ohio valley the governor said he had asked White House and FEMA for additional supplies.

Jeff Black of NBC News contributed to this report.