Durham, N.C. — No criminal charges will be filed in the Dec. 9 wreck involving an Amtrak train and an SUV that left two brothers dead, police said Tuesday.

Calvin Brandon, 9, and Hassan Bingham, 6, both of Durham, were thrown from their mother's Ford Explorer when an Amtrak train bound for Charlotte hit the SUV. Investigators said the boys weren't wearing seat belts.

Their mother, Deborah Peaks Bingham, was treated at Duke University Hospital and released.

An accident report released Tuesday by the Durham Police Department says the crossing arm came down on Deborah Bingham's windshield as she was stuck in traffic at the Ellis Road crossing between Angier Avenue and Pettigrew Street. She tried to back up and move forward to get off the tracks, but the train hit the back end of the Explorer before she could finish maneuvering.

Police spokeswoman Kammie Michael said the train was traveling at 74 mph and couldn't stop in time.

The Explorer spun around, and the two boys were thrown from the vehicle, according to the report. A tire knocked off the SUV flew through the air and hit another car.

Michael said investigators determined the crossing arms were working properly and didn't contribute to the wreck.

The state Department of Transportation installed "Do Not Stop on Tracks" signs at the crossing two days after the wreck to reinforce a safety message for drivers.

Drew Thomas, a DOT crossing safety engineering manager, said officials are trying to determine how to make the crossing safer to prevent future accidents. The DOT could put markings on the pavement in front of the intersection or work with Norfolk Southern to put sensors on the crossing arms so they wouldn't close if they detected a vehicle on the tracks, he said.

The DOT has applied for federal economic stimulus money to try to put an overpass or underpass at the intersection. Officials estimate such a change would cost $13.5 million.