As many as one in five drivers are evading fines because of weaknesses in the fixed penalty system, an investigation has found.
Offenders are getting away with breaking the law because their cars are registered to a company, because officials cannot track them down or because An Post delivers the summons to the wrong address.
The findings were made by the Comptroller and Auditor General Seamus McCarthy, the state's public spending watchdog.
Mr McCarthy has called for the garda to urgently address "significant" shortcomings in the fixed penalty system to make sure it is fair and maintains public confidence.
Motorists are also able to escape fines, penalty points or court appearances by having illegible number plates or because of the wrong details on car ownership are on official systems, he found.
Garda Commissioner Martin Callinan ordered a review into the fixed charge penalty system earlier this year.
The system came under the spotlight after it emerged senior gardai were being probed for mass wiping of penalty points from driving licences.
In its investigation into the fixed penalty system, the Comptroller and Auditor General examined a sample of 300 penalty notices which were later overturned.
Mr McCarthy found there was no apparent reason for quashing the penalties in 4% of cases, while more than half of the cases were cleared for "discretionary" reasons.
The issue of Garda discretion in wiping driving offences was at the centre of controversy over the fixed penalty system.
The public spending watchdog found that excuses accepted by officers for overturning fines and penalty points included:
:: A lack of concentration by the driver who had other issues on his mind, such as a cow dying on his farm.
:: A speeding driver who reasoned that the road was wide and quiet at the time.
:: A motorist who claimed he was hurrying back to a farm because bees were attacking livestock.
:: A driver who was cleared for being on "urgent domestic business".
:: A motorist who was excused because they were late for a swimming lesson.