This is hidden brain.
I'm Shankar Vedantam.
It's a summer evening in northern Indiana.
Three teenagers are in their car, headed to a church sponsored volleyball game.
It's 1978.
The three Ulrich girls, sisters Judy and Lynn, and their cousin Donna, drive down us 33 in a Ford Pinto.
Judy is behind the wheel.
Shes 18, a recent high school graduate, two years older than her little sister Lynn.
Donna is also 18.
Around 630, Judy slows down.
Shes worried she might have left the cap to the gas tank on the trunk.
She puts on her hazard lights.
A few seconds behind the pinto, on the same road, Roger Duggar is, is driving a Chevy van.
He's looking for a cigarette pack on the floor.
When he looks up, the slowing Pinto is right in front of him.
He's going about 50.
He doesn't have time to stop.
At first, Roger doesn't think the crash is that bad.
Then he smells gasoline.
Later, reporters will recount testimony from a third driver who saw what happened.