Manheim Township investigators say 22-year-old Sean Kemberling of Lancaster admitted throwing the folding knife with a 3.5-inch blade.
The alleged incident occurred Saturday when a 53-year-old Lancaster man merged in front of the car in which Kemberling was a passenger.
Police say Kemberling thought his car had been cut off and threw the knife through the victim's open window.
Police traced the suspect car's license plate and found Kemberling at the owner's home.
He is being held in the county prison on aggravated assault and other charges.
