Robert Perago, 53, was arrested after the crash at 6:35 p.m. Saturday at Christina Parkway and South College Avenue.
Police say a Toyota Camry was stopped at the light when Perago slammed into the back of the vehicle with his BMW.
The driver and the front seat passenger of the Camry, a 60-year-old woman and a 65-year-old man, were not seriously injured.
However, 90-year-old Cora Williamson, of Wilmington, was riding in the back seat and was killed.
Police say Perago fled the scene of the crash on foot but, thanks to the help of witnesses, were able to find and arrest him.
Perago was arraigned and released after posting $12,000 cash bail.
Police say this was his 3rd DUI offense.