What car is on the back of an older US 10 dollar bill?

Bills first issued in 1928 had a generic car on the back. According to the Treasury Department, the car isn't a particular model but is merely an artist's interpretation. A lot of people believed it was a model T-Ford or a 1926 Hupmobile but it was actually a composite of multiple cars of that era. Using a particular brand would have been seen as advertising.

Newer $10 bills only show the Treasury Building in a more close-up image. See the BEP website linked below.