Police did not identify the man, who was taken to the Maryland Shock Trauma Center in Baltimore after the 2:30 a.m. crash.
The injured man was approaching Franklin Boulevard in a 1999 Honda when a 2008 Chevrolet also traveling north struck the Honda from behind, police said. Police did not identify the cars' models.
The injured 29-year old was trapped and he was extracted from the vehicle by police.
Police said they suspect alcohol was involved in the crash because "an odor of alcohol was emanating from the Honda driver."
The interstate was closed for about 2 1/2 hours while troopers investigated, police said.