What is the danger of driving too closely behind a large freight truck on an open highway?

1. The truck completely blocks your forward sight distance, and your car is hidden in the truck driver's rear blind spot
2. Following closely saves fuel by drafting, which outweighs the reduced view
3. The truck's air brakes stop it faster than your car, so a short gap is adequate
4. Spray and grit thrown from the truck's tyres are only a cosmetic nuisance