Traffic accidents have been very costly to individuals and societies over long decades, motor vehicle collision may cause serious injuries or even deaths to drivers, passengers, or pedestrians. Vehicle collision also causes car and property damage. However, there are some factors, which contribute more to the risk of car accidents that includes the vehicle itself, speeding, road conditions, and driver skills and behavior. In this work, a factor effect study using design of experiment tools has been performed to study the effect of some factors on the severity of car accidents in a city in the Gulf area over a year. Actual data was gathered and statistically analyzed, the factors considered in this study were basically; speeding, driver's skills and attention during driving, and driving under alcoholic condition besides studying the effect of using seatbelts on accident’s severity level. The effect of the main factors and the factor interaction was analyzed. The study has revealed that 80% of the accidents were caused by low attention and poor skills of drivers; it was also found that fastening seatbelts was very effective in reducing medium-severity accidents.