Background – Thailand has the second highest rates of road traffic mortality globally. Detailed information on the combination of human, vehicle and environmental risks giving rise to each incident is important for addressing risk factors holistically. This paper presents the result of forensic road traffic investigation reports in Thailand and determines risk factor patterns for road traffic injuries.Methods – Detailed forensic reports were extracted for 25 serious traffic accident events. For each report, accidents were characterized by the number of vehicles, number and type of injuries and deaths, road user types, involvement of roadside hazards, medical care provided, and human, vehicular and environmental influences on the incident. The Haddon matrix was used to analyse risk factors in three phases (pre-event, event, post-event) stratified by four agents (human, vehicle, physical and socio-economic environment).Results - The 25 events analyzed involved 407 victims and 47 vehicles. 65.8% of victims were injured, including 22.0% who died. Median age of those injured was 27 years, and 28 years for fatalities. Vehicles crashing with fixed objects, and pickup-related crashes, accounted for the majority of accidents and deaths. Head or neck trauma was the main cause of death. The majority (61%) of deaths occurred at the scene. Human error-related factors included speeding, and drowsiness from night and long-distance driving. Passenger risks included not using seat belt, sitting in cargo area and the cab of pickups. Not having anyone trained in first aid on the scene, first aid being provided by bystanders, and delayed calls to Emergency Medical Services increased injury risk. Overloaded vehicles, unsafe car modifications, no occupant safety equipment, and having unfixed seats were vehicular risks. Environmental risks included fixed objects on the roadside, no traffic lights, no guard rails, no traffic sign, road accident black spots, and hazardous objects roadside.Conclusions - Thailand must address all three temporal phases of the Haddon model and all three factors – human, vehicle and environment. At present traffic accidents cause much avoidable severe injury and death. The Haddon matrix is useful to structure road traffic investigations, revealing multi-level factors common on Thai roads. Keywords: Road traffic injury, Risk factor, Road traffic investigation, Haddon matrix