Unpaid M50 road tolls totalling €3.3m were written off last year.
Documents released to the Public Accounts Committee show that solicitors acting for the National Roads Authority issued 15,000 legal letters and 6,000 civil summonses in 2012.
The figures show that 57% of the vehicles involved were Irish, 28% were from Northern Ireland and 15% were registered internationally.
If the NRA secures a court judgment it can publish the name of a defendant refusing to pay a toll in Stubbs Gazette.
PAC Chairman John McGuinness has called for greater cooperation between agencies to ensure this amount of money is not lost again.