The highest speed can be acquired by going all the way over the dried up river, than backing the Bavaria, and completely jumping straight over the dried up river, after that it'll take almost a expert driver to dodge the debri and than manage to get on the bridge
First time I did it, I was very close to the dried up river, accelerated, then all of a sudden I had enough speed to go to the other side of the bridge and hit another ramp to send me flying to the city side.
All of a sudden, I tried that again, my car flew over the ramp..
I start from the very other side, than jump the river. For some reason you'll gain more speed than usual, but your going so fast the terrain can't load in time