"Please keep calm and be patient on the road, and accept there will be some delays on your journey," O'Brien says.
"Plan ahead, watch your speed and following distances, pay attention to the conditions, stop and take a break if you're feeling tired, and allow plenty of time to get where you are going - especially if you are travelling on roads you don't know."
Police will continue to have a visible presence on our roads this summer, taking enforcement action where necessary.
"But we cannot be everywhere and ultimately drivers have the responsibility to keep their passengers, other road users, and themselves safe this holiday period."
The official Christmas/New Year holiday period ends at 6am on Tuesday January 5.