Yaoundé Nsimalen International Airport is a major civilian hub, while nearby Yaoundé Airport is used by the military. Train lines run west to the port city of Douala and north to N'Gaoundéré. Many bus companies operate from the city; particularly in the Nsam and Mvan districts.  Frequent buses run on the road between Yaoundé and Douala, which has witnessed several fatal accidents. Travel time by road between Douala and Yaounde is approximately 3 hours. Traffic in the city can be heavy during weekdays, but is very light during the weekends. Yaoundé has made significant progress in infrastructure, especially road construction.