Police will travel on trains on the West Coast as part of efforts to reduce the number of fatal crashes at level crossings.
In the past year, there have been five crashes, including three deaths.
Monday marks the start of National Rail Safety week and police are reminding road users that trains weighed thousands of tonnes, they do not stop quickly and they could not turn to avoid people or vehicles on the tracks.
Road policing Sergeant David Cross said officers would work with KiwiRail to identify offending drivers.
Police would ride on trains to keep an eye on problem areas such as Inangahua, Reefton, Westport and Hokitika.
Mr Cross said officers would be particularly vigilant as production increased at the Westland Milk factory.