DALLAS (CBSDFW.COM) – A big rig crash has shutdown the eastbound lanes of Interstate-20 in the southern part of Dallas County.

The driver of the gravel hauler is believed to have hit an overhead sign near St. Augustine Drive just before 9:30 a.m. The impact knocked the sign down, flipped the trailer of the semi on it’s side and spilled large rocks, gravel and hydraulic fluid over the freeway.

(credit: CBSDFW.COM/Chopper 11)

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The closure has eastbound traffic backed up for miles. Click here to check the latest traffic conditions in the area.

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In addition to Dallas Fire Rescue and police, the Texas Department of Transportation (TxDOT) and hazardous materials crews are at the scene.

(credit: CBSDFW.COM/Chopper 11)

There have been no reports of injuries and investigators are still trying to find out what caused the crash.

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Officials with the Dallas County Sheriff’s Office say the freeway will remain closed until the mess can be cleaned up — and they anticipate it being several hours before the highway completely reopens.