By Jim Melwert

PHILADELPHIA (CBS) - After several hours of sitting motionless on northbound I-95, traffic finally started flowing again Wednesday morning.

Pennsylvania State Police say the back-up was the result of a jack-knifed tractor trailer and a fuel spill near the Academy Road exit.

The accident happened at about 3:20 a.m. in the northbound lanes shortly before the Academy Road exit.

Authorities say a tractor-trailer somehow lost control, causing it to jack-knife. The accident caused 110 gallons of fuel to spill onto the roadway.

In addition to removing the tractor-trailer, crews also had to lay down sand to soak up all the fuel.

At about 8 a.m., crews opened up the left lane and by 9 a.m., three lanes of traffic were re-opened. Just about 10 a.m., all lanes were re-opened.

There were no reports of any injuries. The cause of the accident remains under investigation.