Acting road policing manager Inspector Wayne Ewers said the summer months meant more traffic on Northland roads and all drivers need to take extra care.
"Fatigue is one cause of crashes, along with speed, alcohol, and poor driver behaviour through distractions like using a cell phone," Mr Ewers said.
"Northland has had a number of fatal and serious crashes this year where fatigue has played a part."
Police recommend drivers tackling long journeys should get a good night's sleep before driving, share the driving when possible and include rest breaks at least every two hours.
Mr Ewers encouraged motorists to call 555 if they observed driver behaviour that was inappropriate, as vehicles weaving within their own lanes and speed variations could be signs of fatigue.