THE B-double crash that killed a sleeping 11-year-old boy on the NSW mid-north coast was most likely caused by another vehicle's drunk driver, who had a blood alcohol content almost five times the legal limit.

Max McGregor, from Penrith, was killed when a truck crashed into the bedroom of his family's holiday house on the Pacific Highway at Urunga. But police believe the freight truck was swerving to avoid a Holden Commodore ute being driven on the wrong side of the road.

The ute's driver, 38-year-old David Levett, was killed in the crash and police have revealed he had a high-range blood alcohol concentration of 0.245 - almost five times the legal limit. Speed is not believed to have played a part in the accident.

The mid-north coast crash investigations unit is continuing inquiries into the circumstances of the smash.

Max's parents, brother and two neighbours received minor injuries and were taken to Coffs Harbour Hospital. The truck driver and his male passenger suffered chest injuries and were also taken to the hospital.

Last year, 62 fatal crashes on NSW roads involved alcohol, according to the RTA. That figure was down about 15 per cent on the previous three years' averages, when about 73 fatal crashes involved alcohol.

The vast majority of fatal accidents on NSW roads do not involve alcohol, with about 40 per cent of fatalities caused by excessive speed.

A further 19 per cent of all deaths on the state's roads are caused at least in part by fatigue.