Time between road crash and road death?
A study by medical experts in European high-income countries found that about 50% of deaths from road traffic crashes occurred within minutes, either at the scene or while in transit to hospital. For those patients taken to hospital, around 15% of deaths occurred within 1-4 hours after the crash, but around 35%, occurred after four hours .
Three phases of deaths from severe injury
Phase 1.Deaths occur immediately or occur quickly as a result of overwhelming injury
Phase 2. Deaths occur during the intermediate or sub-acute phase. These deaths occur within several hours of the event and are frequently the result of treatable conditions
Phase 3. Deaths are delayed. Deaths during this phase often occur days or weeks after the initial injury and are the result of infection, multisystem failure or other late complications of trauma.
World Health Organization, 2005
In reality, as the World Report on Road Traffic Injury Prevention  underlined, there is not so much a “golden hour”  in which interventions have to take place as a chain of opportunities for intervening across a longer timescale. A comparative study of mortality among seriously injured patients across a range of countries found that for low-income and middle-income countries, the vast majority of deaths occurred in the pre-hospital phase .