How long have automobiles been legally required to have windshield wipers?

Question

How long have automobiles been legally required to have windshield wipers?

Answer 1

Since 1951

Answer 2

I think that depends on your state but I found this info: Mary Anderson is said to have invented the windshield wiper swinging arm in the United States, where she patented the idea in 1905. The idea was initially met with resistance, but was a standard feature on all American cars by 1916."

Thats at least some info