All drivers involved in serious crashes will face automatic breath-testing from January.
The new law was due to come into force in July, but was delayed until next September to coincide with new, lower drink-driving limits.
However, Transport Minister Noel Dempsey decided to push through the special legislation next month.
The old law said gardaí may carry out breath-testing at the scene of an accident, but this provision has been removed in the new Road Traffic Act 2010.