The study examines the causal factors of road traffic crashes in some selected states in South western part of Nigeria. Data were obtained from a total of 352 respondents, from four out of six states that made up of southwestern Nigeria using stratified random sampling technique. Regression Analysis was adopted in analyzing the data obtained. This was done in order to establish the relationship between human characteristics, vehicular characteristics,roadway characteristics,environmental characteristics, and road traffic crashes in the study areas. Based on the findings of the study, it was concluded that human, vehicle, roadway and environment had significant contribution of about 79.4% on the road traffic crashes in the study area.