The shooter told investigators the two drivers got into an argument while waiting at a red light in the Crescentville section of Philadelphia.
Chief Inspector Scott Small said, "It appears that the motive of the shooting is road rage."
The shooter told investigators the man he shot was kicking his car and threatening him before he pulled the trigger.
About a half hour later, the shooting victim was found in his car less than a mile away. He was taken to Einstein Hospital in critical condition.
The shooter was taken in by police for questioning.
"Preliminary investigation does reveal that the 70-year-old man does have a valid permit to carry," said Chief Inspector Small.
People who live near the shooting scene question if the shooting was justified.
"Just because you have a permit to carry doesn't mean you're allowed to. That situation could have easily been avoided. Drive away," said Maria Colon, who heard the commotion outside her window.
RELATED: 8 tips to help drivers avoid road rage
Police are not releasing much information about the apparent road rage encounter and subsequent shooting, saying the investigation is "ongoing."
The shooting victim is in critical condition. The man who fired the gun has not been charged with any crime.
QUIZ: Are you causing road rage?