The main local and regional bus station of Utrecht is located adjacent to Utrecht Centraal railway station, at the East and West entrances. Due to large scale renovation and construction works at the railway station, the station's bus stops are changing frequently. As a general rule, westbound buses depart from the bus station on the west entrance, other buses from the east side station. Local buses in Utrecht are operated by Qbuzz – its services include a high-frequency service to the Uithof university district. The local bus fleet is one of Europe's cleanest, using only buses compliant with the Euro-VI standard as well as electric buses for inner city transport. Regional buses from the city are operated by Arriva and Connexxion.