Fifteen people, mostly policemen, were killed Sunday when their vehicle smashed into a truck on the highway between Cairo and Alexandria, police said. At least 20 other people were wounded in the crash, which occurred shortly after nightfall on the main highway linking the Egyptian capital with the northern city on the Mediterranean coast, said the police official. The policemen were on their way back from a camp near Cairo when their vehicle ran into a truck, the official added. It was not immediately clear what caused the crash. Road accidents are very common in Egypt due to bad roads and poor enforcement of traffic laws. Police estimate road accidents kill about 6,000 people annually.