Two major studies of motor vehicle crash causes were conducted in 2001-7 in the USA. One focused on large trucks and the other on passenger vehicles. In both studies the drivers were assigned the critical reasons for the crashes in about 90 per cent of the cases. Relative risk analyses of the data found that driver distraction/inattention was the second most dangerous driver error for both large trucks and passenger vehicles - following travelling too fast for conditions for large trucks and inadequate surveillance for passenger vehicles. Logistic regression analysis found distraction/inattention were significant problems, and that conversation, hours driving, fatigue and work pressure are factors that lead to distraction and inattention.