Gardaí, politicians and road safety campaigners are hoping for a major change in driver behaviour as a result of the new Road Traffic Act, which came into force at midnight.
The legislation bans motorists from using hand-held mobile phones and allows gardaí to conduct random breath tests to crack down on drink-driving.
It also paves the way for the introduction of a widespread system of speed cameras.
The Government is hailing the measures as a major development in road safety, but opposition politicians say nothing will change unless gardaí are given the resources they need to implement the new laws.