Road accident investigation is the scientific processes conducted by multidisciplinary. The objective is to find the causes of road accidents by considered 3 risk factors: human error, road/environment defect and vehicle defect. Relationship between the causes of road accidents and three time intervals: pre-crash, crash and post-crash were shown in Haddon’s matrix. Nakhon Si Thammarat is the pilot province which received the fund for establishment the Road Accident Investigation Unit at the provincial level and has performed up to date. Road crash among pick- up truck, public van and motorcycle were selected as a case study due to 3 passengers of public van died and 6 injuries in this event. The results of road accident investigation showed that the risk factors of public van driver and pick- up truck driver drove with excessive speed over the speed limit and changing lane abruptly. Recommendations were presented to reduction of exposure to risk of road accident and severity injury.
Keywords : Road accident investigation, Risk factors, Equivalent barrier speed