"When you combine sunstrike with busy intersections, if we're not careful it can be absolutely tragic," Mr Greally said.
People needed to be cautious with their following distances and make sure their windscreens were clean when the sun was lower in the sky.
Black ice can be hard to see, Mr Greally said, but lowering speeds and not being distracted could help to avoid crashes.
Mr Greally said the circumstances around the four fatalities over the weekend were not yet clear.
"It's a hell of a shame. We always say when a person loses their life on our roads it is one person too many ... it's completely avoidable and entirely unnecessary."
Last night, Feilding man Kent James Bond was identified as the driver of a car that lost control and died in a head-on collision with an SUV near Palmerston North on Saturday.
The crash involved a car and an SUV which was towing a large horse float about 2pm Saturday on State Highway 3 in the passing lane near Sanson.
Police said it appeared Mr Bond had overtaken a number of vehicles in the westbound passing lane before losing control and crossing the double yellow lines, directly into the path of an oncoming SUV.
The SUV and horse float jack-knifed and rolled as a result, trapping all four occupants in the vehicle which then caught fire.
Other motorists braved flames to free the SUV driver and three passengers from the burning vehicle.
The four injured people were taken to Palmerston North Hospital, one person in critical condition.
Police said they would conduct a detailed investigation into the crash but indications suggested excessive speed was a factor.
Yesterday evening, a motorcyclist died after colliding with a ute in South Auckland.
Police said the crash happened on Constable Rd, Waiuku, shortly before 6pm, and the serious crash unit would now be investigating.
A woman also died following a crash in Levin last night.
Police said the accident happened when two vehicles collided at the intersection of State Highway 57 and Waihou Road.
Both cars had single occupants and the driver of the other vehicle was taken to Palmerston North hospital.
On Saturday, a motorcyclist who police said had not been wearing a helmet died in Moerewa, Northland.
Police said the 30-year-old man, from Moerewa, was riding a friend's motorcycle on Mason Ave about 4.35am on Saturday, and came off the motorbike when he drove on to grass and hit a fence post.
The man had been unconscious when an ambulance arrived and he was transported to Whangarei Hospital, where he died about 5.15pm on Saturday.
A number of other motorists suffered injuries in vehicle crashes at the weekend.
A car with four occupants rolled on the western side of Lake Taupo and down a bank 10km south of the Waihaha River about 12.26pm yesterday.
Police said some of the four occupants suffered from minor injuries.
A road near Taupo was also closed yesterday afternoon after a truck caught on fire.
Emergency services were called to the scene on State Highway 1, 11km south of Taupo, after the truck lost an axle and caught fire.
According to Ministry of Transport data, as of today 172 people have died on roads this year, an increase of 13 deaths on last year's toll at the same date of 159 fatalities.
