Wellington is served by State Highway 1 in the west and State Highway 2 in the east, meeting at the Ngauranga Interchange north of the city centre, where SH 1 runs through the city to the airport. There is one other state highway in the region: State Highway 58 which provides a direct connection between the Hutt Valley and Porirua. Road access into the capital is constrained by the mountainous terrain – between Wellington and the Kapiti Coast, SH 1 travels along the Centennial Highway, a narrow section of road, and between Wellington and Wairarapa SH 2 transverses the Rimutaka Ranges on a similar narrow winding road. Wellington has two motorways, both part of SH 1: the Johnsonville–Porirua Motorway and the Wellington Urban Motorway, which in combination with a small non-motorway section in the Ngauranga Gorge connect Porirua with Wellington city. A third motorway, the Transmission Gully Motorway, is planned to open in late 2021.