The northbound lanes began to reopen around 5:30 p.m. The southbound lanes remain closed until around 7:30 p.m.
The closures came after a gasoline tanker truck crashed, overturned and leaked thousands of gallons of fuel on the road.
It happened before 8:30 a.m. Wednesday near New Discovery Road.
Delaware State Police say the 49-year-old truck driver from Vineland, New Jersey lost control trying to avoid a van that had crossed lanes.
That van, with a 55-year-old Dover man at the wheel, was pulling a car trailer while traveling on the northbound side of the highway.
"At some point the right rear tire of the Chevy van blew out, causing the operator to lose control of his vehicle. The vehicle, in turn, crossed the center median and traveled into the southbound lanes of Route 1," said Master Corporal Michael Austin of Delaware State Police.
That van went into the path of the tractor-trailer that was hauling 8,900 gallons of fuel. When it overturned, the highly-flammable gasoline started leaking out.
Video from Chopper 6 HD showed steady streams of gasoline pouring from parts of the ruptured tanker.
The truck driver was helped out of the cab by other motorists and airlifted to Christiana Hospital to be treated for injuries described as serious.
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