I do not believe that the motorcade turned right. I think they disappeared from sight once they went over the railroad tracks at the top of the hill, and turned left just as J.W. Courson mentioned to Larry Sneed, as published in "No More Silence". Here is a 1968 aerial photo of Stemmons, showing Parkland, the Trade Mart, the railroad crossing which we see the LBJ car and his SS car along with several motorcycles drive over so fast that the wheels left the ground according to some of the occupants in the film, the TSBD in top right of photograph, and where the limousine was located, having just exited Stemmons Freeway, and in front of an underpass(Circled in redon the photograpgh) and about to make a right turn.