The busy period on the roads for holiday travellers in and out of Auckland is expected to start today, with 5,000 to 8,000 more vehicles on the road daily.
Regional highways and roads are traditionally clogged on Boxing Day, the NZ Transport Agency says.
"This is one of our busiest times of the year - the time when Aucklanders head north and south for their holidays and the city's Christmas sales start," agency highway manager Tommy Parker said.
The Northern Gateway Toll Road on SH1, north of Auckland, would be one of the busiest roads, he said. It usually hosts 15,000 trips a day but averaged almost 20,000 a day over Christmas last year. Its busiest day, January 2, totalled 23,500 trips.
Mr Parker stressed the need for drivers to plan their trips and allow plenty of time for a safe journey.
The proportion of crashes on open roads that result in injury increases from 39 per cent year-round to 54 per cent over the holiday period, police statistics reveal. For serious or fatal crashes, this increases from 51 per cent to 66 per cent.