Backes went to all that trouble to show a police car exiting via Main Street. But, why bother? Everybody already knew that Lt. Rio "Sam" Pierce went out that way, and it was the pretense for Ruby getting in. Officer Roy Vaughan had to go clear the way for Pierce and that's when Ruby slipped in. Isn't that the story? So, what did we need to see the other for? We didn't.
A large crowd was gathered at the Commerce Street ramp to view Oswald, and that was consistent with the publicly announced plan of taking him that way. There was no reason for anyone to think otherwise.
So, what were those guys at Main Street doing? Hoping that the police lied, or that there would be a last second switch, and he would be driven out the entrance? Since when do good citizens treat police announcements with such doubt and suspicion?