I'd ask myself: what am I doing in a car with this man that I know to be a reckless driver?
Given a choice I wouldn't go with him, but if they forced me to do it, I'd try to save him from crashing because who knows what will happen. Maybe he gets stuck and the car catches fire and I'll have to watch him burn... You never know what consequences your actions will bring so it's best to go with your gut and ethics. This way whatever happens you'll be able to justify your actions.
Well, it's a small bridge after a turn in a neighborhood, so the car will be going like 20 mph. There will be damage to the car, and the bad driver will deservedly lose driving priviledges but the only damage will be to property. Should have been clearer in the OP.
I see this action, letting the accident happen, as the most ethical one.
It reminds me of that good old debate about the necessity of stopping drunk or reckless drivers. There are people who believe that if you see someone zigzagging and you're sure he's DUI, you should somehow cut him off and make him stop so that he doesn't get into an accident, but while doing so you may be the cause of his accident.
I've always found this too risky and thought that the best approach is to call the cops, give them his plates and wereabouts and let them handle it. I wouldn't endanger myself and my car just to stop him.