No, unfortunately their isn't. There is only two ways to get across to the other side of the city. My first suggestion is rather simple. Play the missions until you unlock the bridge. The other is to use the 'car float on water' cheat(Right, R2, Circle, R1, L2, Sqaure, R1, R2). You must be in the car for this cheat to work(and do not get out).
You can do this by completing more and more missions.then automatically the bridges will open...
I don't know of any cheats for that other than flying cars :P I just turn that one on and fly wherever I want to go if I don't have the rest of the city unlocked. The beginning of the game doesn't take too long to beat so you might as well just unlock em normally. I know if you have means of transferring memory card data from a computer people put their saved games up on the internet in some places.