What caused the car crash?

it was the earring caught on her sweater.
yes, it had significance is the effect that the father was a nice guy and wasn't committing murder/suicide.

i'm proud to admit to never have watched a "reality" tv program!

I only first saw this movie tonight so I am not being influenced by by the analysis of others. I believe the flashback in the car was one of the true events in the movie, because no one lived to recount that part of of the story. The movie provides varying accounts on how the accident may have occurred, but finally we were treated to the actual version: The husband was very happy and at peace with his decision to kill both of them. His head was turned sideways nearly the entire time while he was driving. He intended to crash into anything that came along, regardless of whether other innocent people were killed. He crashed their car while he was tenderly staring at a momento on his wife's blouse, and no one but the author could have derived this detail.

Saw the DVD last evening and found it to be very thought provoking and contemporary as to current events in our world today. As to the cause of the crash, I cannot accept that the husband's careless driving was deliberate and he wanted to "crash into anything". He was acting in a very careless way, probably due to the alcohol earlier. The reaching for the pin was just stupid with tragic results.
I agree that the brother's guilt was assumed by his refusal to answer the phone and return to the house as requested by his sister's earnest plea.

According to what Sabine told Tom, Sami had an eye condition that was supposed to keep him from driving at night. Unfortunately, with Rachel having had too much to drink, Sami had to drive. But, it seemed to me that his trying to untangle the pin from Rachel's sweater, which took his eyes off the road, is what caused the crash. So, I don't think it would have made a difference if his vision had been 20/20.

Emperor: Tell me how he died.
Captain Algren: I will tell you...how he lived.