Morgan Lake, 22, of Calvert City, Md., had just driven onto the bridge Friday night when a tractor-trailer rig struck her car twice, knocking it onto a railing where it hung briefly before falling into the bay, The Washington Post reported Sunday.
Lake said the drop "felt like eternity."
When the car hit the water, the driver's side window and the windshield shattered and the vehicle immediately began filling with water, Lake said.
At first she felt as if she would die, she said.
"I got myself together. I went from panic to calm."
Lake unbuckled herself, pushed through the broken window and swam to the surface.
A boater went to Lake's aid and stayed with her until a boat from the Maryland Natural Resources Police took her to shore and she was transferred to a hospital.
Lake was released from the Maryland Shock Trauma Center in Baltimore Saturday with bumps and bruises, the Post reported.