Four in every 10 cars written-off by insurance companies end up back on the roads.
The Road Safety Authority (RSA) says that some 45,000 vehicles every year are deemed too expensive to repair, but 18,000 return to use.
And chief executive Moyagh Murdock told the Dáil Transport Committee that vehicle defects had contributed to 3pc of all fatal collisions and 1.5pc of serious injury collisions between 2007 and 2012.
During this period, some 1,145 people died on the roads. Vehicle defects are linked to 42 of these fatalities.
The comments came after an inquest heard this week that a car which crashed last year killing a child and three women was not roadworthy, despite passing an NCT three months earlier.
Ms Murdock added that worn and inappropriately inflated tyres contributed to collisions "to a greater extent than previously thought". She said new legislation would provide a register of vehicles written off because they were not roadworthy and unsafe to drive.