The jump isn't what typically kills you when you jump from a bridge, instead what happens is you break your legs and other bones, causing you a tremendous amount of pain, and leaving you crippled as you drown to death while your body screams at you in pain.

As far as suicide goes it's a pretty fucking brutal way to go, and it's also a good explanation of why men end up successfully committing suicide more than women. Men go with guns or throwing themselves off buildings which don't leave a lot of room for error and are based on one single impulse after which you can't go back (pulling the trigger/jumping), and based on what people who survive jumping off bridges feel almost everyone I've heard talk about it has said they felt instant regret while falling and the desperation to continue living. Women tend to take tablets or slit their wrists which takes a decent amount of time to kill you during which you can actually solve the issue and stop your own death.