Personally, I'd have to say that I am different. If I didn't see emergency vehicles at the scene of an obvious wreck, with obviously injured people, I'd have to say I'd get the hell out my car right after I dialed 911, which is why I find his story hard to believe. It's absurd to think a multitude of human beings would just casually ignore that kind of a disaster and not help without first being persuaded by the injured. I'm sorry, I'm not saying it didn't happen that way, but one has to admit that's a pretty tall story.
Sorry, it's the other way around and it's not absurd at all when you think about it. If the accident happened right in front of you, it's different than if you were the 15th car to go by. You might find yourself thinking, "gee, they didn't stop, what do they know that I don't?" It's not that people are callous or don't care, they want to help, but when the external stimuli suggests that no one else is helping, people factor that into their judgement. Plus, with cars, you are already moving as a group and if you stop, you stop traffic. We aren't the rugged individuals we all think we are.
Think about it another way. You are walking down a busy street. A person is sitting on a sidewalk convulsing and shaking but none of the 50 people walking by do anything, would you? Conversely, imagine yourself walking on a trail and you see the same thing. Who is more likely to get your help? The author cites studies (they faked epileptic fits) on this and with one person help was given 85% of the time whereas with 5 it was only 31% of the time.
Get the book, it's by Robert B. Cialdini and it's called "The Psychology of Persuasion" and he's dead on with this and a lot of other things.
It's a great read and now I'll go find a psychology forum.