When I first moved to Treasure Island, I only had a few months' experience riding, and you bet your ass I tried that 15mph exit in a car a few times before I went near it on a bike, and even then I had a roommate in her car behind me just in case.
But that's sortof an unusual scenario, I was really super green at the time. These days I'm not sure there's much I could learn about a road in a car that's really going to give me any advantage. A road that's going to be a serious challenge to me on a bike is probably gonna be a little tricky in a car too come to think of it, especially since I'm a tad rusty on 4-wheeling it.
Now that I'm used to the Treasure Island exit, I know I can brake to pretty much a dead stop in the distance between splitting off from the lanes to the point before the 15mph exit really starts to curve, so I don't worry about it much even when somebody's tailgating me (although I do HATE that, especially that one time there was a bus stalled out in the middle of the exit, and I had a passenger on back. He knows what hard braking feels like now, oye)