There are no stairs on the overpass. The pathway leads to the parking lot behind the fence. All the police or the railroad workers needed was a line of sight and all of it is very short distances.
People reported smoke in a parking lot which isn’t that unusual. I have to remember how smoky a 1950’s and 1960’s car was. Notice no one mentions muzzle blasts or orange flashes.
The people running toward the parking lot and picket fence were trying to catch a glimpse of the limo as it drove north on I-35 on it’s way to Parkland Hospital. The triple bypass is part of the exchange for the highway. One lane goes north, the other south and the middle continues west.
The smoke was not from the parking lot. I think smoke was reported from the front of the bushes.
I think in order to see the report they would have had to be looking there sooner. They would have most likely been looking at the president's car until they heard a shot.
I don't remember anyone saying they were running up the knoll to see the car. Was the cop leaving his vehicle to run up the knoll and look at the limo? If I had a citation, I would read it.