King Abdulaziz road in Jeddah, Saudi Arabia is the main road connecting the city’s south and north points. Unfortunately, there are many accidents on this road, resulting in financial damages, disabilities, and deaths. We noticed that the location of the service road entrances to the main road do not allow drivers to reach the U-turn safely. They, along with the U-turn exit and exit off the road, are close to each other. In addition, the length of the U-turn sections on both sides needs modification. This research solves this problem through mathematical calculations (equations of motion) while making assumptions based on safe and effective driving. We made a theoretical model, based on a car with poor acceleration, which needs more distance to work with than other cars. This model calculates the ideal distance needed for this car to enter the main road via the service road up to the U-turn then exit the road on the other side safely. That is calculating enough space for this car to change lanes, reduce speed to turn, and accelerate to join the road after turning. This result suggests a minimum length between the entry to the main road and the U-turn, the U-turn and the exit off the main road, and the length for different parts of the U-turn. We then compared these measurements with eleven important U-turns on this road. The comparison shows significant difference with most of them; thus they need modifications. This would hopefully reduce both accidents and congestion.

equations of motion, highways, road safety, traffic engineering, U-turns.