The Waikato Expressway north of Te Kauwhata has largely been built on the existing line of SH 1N, although at Pōkeno the highway was diverted to bypass the town to the east. South of Te Kauwhata, most of the expressway has been built on a new line bypassing the towns of Ohinewai, Ngāruawāhia, Te Rapa and Cambridge, with old sections of SH 1N reverting to local arterial roads. The former route between Taupiri and Horotiu via Ngāruawāhia was temporarily re-designated State Highway 1G before it could be transferred to the Waikato District Council.