The main highway passing through San Salvador is the CA-1 (Pan-American highway), which at one point becomes Bulevar Arturo Castellanos. The RN-21 (Bulevar Monseñor Romero) is a major east–west road connecting the cities of Santa Tecla and Antiguo Cuscatlán, finally merging in San Salvador with the RN-5 East/West (also known as Bulevar los Próceres), that later turns into the North/South RN-5 heading towards the International Airport. Another major roadway is the RN-4 (Carretera Este Oeste) which runs from San Salvador through Apopa, and subsequently merges with the CA-1 Panamericana.