This study is aimed to evaluate Road Traffic Accidents (RTA) in Addis Ababa– Adama Expressway which is the first modern expressway in Ethiopia. The study analyzed 1,137 accident data that occurred in the past three years and eight months since the launching of the project. The study investigated several characteristics of accidents. Among others, this includes accident type and severity, time of accident occurrence and types and level of traffic. Advanced statistical tests were conducted to identify the contribution of accident instruments. Out of 1,137 RTA datasets, 75% occurred during day time and about 24% of accidents occurred at night. The highest fatality accident occurred in January. In total, 84 fatalities, 191 serious injuries, and 438 light injuries were registered. The highest number of serious injuries (about 38%) occurred during the weekend. A total of 1,348 vehicles were involved in road accidents. About 33.5% of accidents occurred due to rear-end collision while about 31% occurred due to vehicle rollover. The remaining accidents occurred due to collision to the guardrail and curbstone about 39% of accidents occurred due to unethical driving behavior while about 19% of accidents occurred due to over speeding. In addition, driver fatigue, flat tires, poor vehicle brake performance, and steering problems, the presence of animals were also contributing factors to the reported accidents. The study recommended remedial Measures for the safe operation of the expressway.