One driver commented the traffic had been at a crawl for about two hours just north of Paraparaumu, with cars travelling at a speed of around 10km/h.
The same route had been heavily congested on Wednesday, with the agency reporting traffic did not ease until about 7pm.
Unlike on Wednesday, Paekākāriki Hill would be open on Christmas eve.
Earlier in the day the transport agency had also asked travellers to plan ahead for roadworks on SH1 at Mackays Crossing.
With the Wellington region also hit with wet weather on Thursday, MetService meteorologist Lewis Ferries recommended travellers allow plenty of time to drive to the conditions.