Green’s Dictionary of Slang

(US) a car used by criminals escaping from a crime.

1930		E.H. Lavine Third Degree (1931) 129: The stolen get-away Cadillac car had plates calling for a Ford automobile.
1938		R. Chandler ‘Red Wind’ in Red Wind (1946) 52: Waldo had a getaway car parked outside the cocktail bar where he was killed, unlocked with the motor running.
1955		‘Blackie’ Audett Rap Sheet 83: Then we would plan our way out and stash the get-away cars well out along the road.
1969		P. Theroux Murder in Mount Holly (1999) 87: Oh, botheration! [...] How can I drive the getaway car if I can’t drive?
1973		Batman No. 251 20: He has a getaway car ... with balloon tires for riding on sand!
1985		L.L. King Warning 26: Behind the getaway car, the pursuing vehicles broke down with flat tires.
1997		M. Balousek 50 Wisconsin Crimes of the Century 195: The bandits grabbed a female bank teller, hoping to use her as a shield so they could reach their getaway car.
2004		D.J. Frantsve Celtic Phoenix 12: With the getaway car at the back door, driver in place, [and] engine running.