The Policing Authority says there is evidence of failure to conduct breath tests at serious and fatal road collisions.
It says 42% of drivers are not tested after serious injury crashes and 22% are not tested after fatal collisions.
Two reports relating to Garda performance have been published by the authority today.
They show that crime is up in all groups except homicide, and detection rates have fallen for the second year in a row.
The authority notes that the increase in the number of crimes "may reflect increased confidence in reporting crime to the gardaí which is to be welcomed, especially in the case of sexual crime".
Chief Executive of the Policing Authority Helen Hall says these issues need to be addressed.
She explained: "The fall in detections has been a cause of concern for quite a period, and you can really see that continuing - that's something that needs an organisation wide focus on that.
"Another big concern is in relation to the failure to conduct breath testing at serious and fatal road collisions."