spoken English

They can be spoken but it would make for stiff conversation.

I got your stiff conversation right here.

I might say "All traffic must stop when the light turns red." Or, "Cars have to stop when the traffic light turns red."

Truthfully, I rarely hear people say 'traffic' as in 'traffic light'. We take it in context. Also, around HERE we don't conversationally say vehicles unless we're in court or a police man, maybe. In other parts of the country vehicle is probably more common (maybe the traffic in traffic lights is more common elsewhere too).

You can use either. Might make a stiff conversation for some, but don't worry about it. If you're in Boston, they'll probably think you are from Kansas City.

Oh! And I was being good too.