“Where A Private Road (from A Gasstation) Meets A Highway”

Was charge with "disobeying" a no left turn from a private drive to a public highway

Is the traffic sign valid when at a meeting of a private road and public?

is this defined as being a highway? (the private road)

COP said that their no left sign was on public property --- therefore ok

my issue is if any private drive is a "legal intersection" and a highway

Thanks