The following info re the motorcade stopping on the Stemmons onramp is from the www & forums.
DPD Officer Earle Brown, on the railway overpass above Stemmons, told Earl Golz in March 1980 that he saw the limo and 4 other cars stop on the Stemmons on-ramp for at least 30 secs.
Brown later repeated his story for Gary Mack.
Officer Doug Jackson told Mack in 1981 that he and Chaney raced after the lead car, caught up with it after about 30 secs, and Chaney spoke through the window to Curry.
Curry told another researcher in 1979 that Chaney caught up with him as they began climbing the Stemmons on-ramp.
Curry told Mack that he slowed down in order to find out if anyone had been hit, as he was unaware that anyone had been hit until Chaney told him.
He also said he then had to tell the limousine driver, Secret Service agent Bill Greer, how to get to Parkland Hospital, before issuing “Go to hospital” order.
Curry told the Warren Commission that he did not transmit on Channel 2 until after he spoke to Motorcycle Officer Jim Chaney.
DPD Officer Courson said the lead car had slowed sufficiently for him to catch it on the Stemmons access road, and Courson was 100-120 feet behind McLain in the motorcade, and McLain was himself about 140 feet behind the Presidential limo when the shots were fired. Courson was approx. 80 yds behind JFK at Z-313.
So, it makes sense that the JFK limo stopped for at least 30 sec on the onramp,
to get directions from the SSA agents on Queen Mary, which also stopped (probably side by side).
Both limos turned off their flashing lights & sirens so that they could converse (Hoffman).
Using their radios would have been quicker, but would have been public & embarrassing.
Why did Curry (in the lead car) stop on the onramp & ask Officer Chaney if anyone had been hurt?
Curry could have driven up to the rear of the 2 limos & asked them directly.
But i suppose that Curry did not suspect that JFK & Connally had been shot, Curry was probly only worried about the general public etc getting shot.
JFK & Connally ducking down out of sight was of no concern.
Anyhow, it appears that the guys in Queen Mary were no wiser re the best way to get to Parklands.
So, Greer & Kellerman must have hollered to Curry & Co when the lead car finally reached the limos.
Curry then probly told Greer to follow the lead car, & the lead car probly took the lead again (Curry was the driver).
And it makes sense that the JFK limo was stopped for at least 30 sec.