The planners of the vist to Dallas wanted to go through downtown without the turn by the TSBD. In fact, the turn was put in AFTER they landed as it would be easier to get to the Stemmons Freeway from Elm rather than through Main Street to get to the Convention Center where Kennedy was to deliver a speech. This was totally against SS protocol for no turns at less than 30 mph or greater than 90 degrees.
If you look at the Zapruder film you see people running across the grass to see the motorcade. They were lined up on Main waiting and ran to the other side.