BROOKLYN - An overturned tractor-trailer on the eastbound Brooklyn-Queens Expressway created commuter chaos for the Wednesday morning rush.  

The semi-truck flipped over near the Atlantic Avenue exit in Brooklyn Heights at around 4:30 a.m., and wasn't cleared until 7 a.m.  

Another vehicle was involved, and one man was taken to Bellevue Hospital in serious condition. 

Chopper 12 was overhead after the crash, which temporarily shut down the roadway and backed up traffic for miles in both directions. 

It remains unclear what caused the accident.