Wellington and Porirua are linked by State Highway 1 (SH1). Road improvements have progressively reduced travel times between Wellington and Porirua and increased the demand for housing development in Porirua. In 1940, the Centennial Highway developments saw the opening of a four-lane high-speed highway in Ngauranga Gorge bypassing the slower routes through Ngaio and Khandallah. During the 1950s, the high-speed Johnsonville–Porirua Motorway was built through Tawa on the eastern side of the valley. The first section from Johnsonville to the Tawa turnoff at Takapu Road at the southern entrance to Tawa opened on 15 December 1951, broadly following the line of the old North Island Main Trunk railway. It reduced road travel times and considerably improved access between Wellington and Porirua by eliminating the need to use the narrow winding road through the bottom of the Tawa valley in the Glenside area. The second section, from Takapu Road to Porirua, opened about 1956 and allowed through traffic to bypass the lower speed road through Tawa. The Johnsonville bypass connecting the south end of the motorway to the top of Ngauranga Gorge opened about 1958 completing the four-lane road link between Wellington and Porirua.