Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

Here's a 1963 Mercury like the one in the motorcade.

Notice that the driver has the window wide open. It's all the way down. He's got his elbow out. But the vent window is closed. 

Don't you think it's typical that if you've got the main window rolled all the way down that you don't bother opening the vent window? How much air do you need?

Observe that that was also the case on the driver's side of the car in question:

Main window open; vent window closed. Now, what was happening on the other side of the car. Consider that it was a very warm day, unseasonably warm for late November. Jackie complained about the heat. There were big three men sitting astride in that front seat, crammed in there, with LBJ's personal assistant Cliff Carter in the middle. So, that's three big men sitting on the bench seat of normal-sized sedan on a hot day. Don't you think that the main window on the other side was also wide open, as it was on the driver's side. You don't think that one was wide open and the other was closed, do you? Isn't the whole idea to get cross ventilation? 

So, if that window was also wide open, as we can assume, then why bother opening the vent window? The driver didn't do it.