Northland road policing manager Inspector Murray Hodson is also cautioning drivers after a man crashed while driving through the roadworks on Saturday.
The 44-year-old was heading south about 7.20pm when his car drifted over the centre line and back into the left-hand lane before sliding off the road, hitting road cones and roadworks signs.
He was charged with operating a vehicle carelessly and refusing to give blood, and will appear in the Whangarei District Court tomorrow.
Mr Hodson said: "My main message is that the reduced speed limit is so the safety of all road users is maintained at all times. Police will be monitoring that road until such time as the repairs have been completed.
"All I'm asking for is the drivers to have patience. It is extremely dangerous in its current condition."
Friday's fatal crash came after a 6-year-old boy died near Waipu this month. Northland's road toll for the year now stands at 14.