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.
The top two stations for wiping out fines or penalty points were both in Dublin - Blanchardstown with 699 and Bridewell with 355.
The others making up the top 10 were Kevin St and Pearse St in Dublin, Ennis, Co Clare, Ballymun, Navan, Coolock in Dublin, Henry Street in Limerick, Fitzgibbon Street in Dublin and Mullingar.
In Blanchardstown, the Bridewell, Kevin St, Fitzgibbon St and Navan more than half the cases were outside their division.
The report found that in more than 300 cases penalty points should have been recorded on a driver's licence but the Garda record did not match the state's National Driver Vehicle File (NDVF).
The C&AG said there was no excuse for mismatch as the file is the official record and is updated and sent to the Garda every week.
It also found a significant number of the 3,000 notices became statute barred because of delays getting data into the Garda system from notepads and devices.
Lax use of garda notepads was also identified as an issue, with pages going missing or spoiled.
The C&AG inquiry has found a high level of unaccounted for forms used to tell drivers they face a penalty and officers not being required to account for all used or missing forms.
The commissioner has agreed to document every case were fines or points are not enforced by an officer and get reasons for spoilage.
One in nine offences dealt with by a fixed charge went unpaid but the driver did not end up in court because a summons was not served by a garda. The C&AG warned that some offenders may have worked out how to dodge a summons being served.
He called for closer links with the courts service and its case tracking to monitor cases.
The report found that senior officers with the facility to terminate cases on the fixed charge system are not restricted to doing so only for cases within their line of management, their district or unit.
The C&AG found evidence that the policy on wiping out points and fines is not being applied consistently with a "significant proportion" not satisfying the rules.
He found the high levels cannot reflect "exceptional circumstances".
The C&AG warned of his concerns that "absent and inadequate records, and recorded facts in other cases, give rise to concerns that many cases have been terminated without due cause".
The investigation found that the state is losing around 1.12 million euro every year because drivers using company cars are able to evade penalties.
Where a company owns a car, it is legally obliged to identity the driver in charge of the car at the time an offence was detected.
But many frequently respond that they do not know who was driving.
Nearly a quarter of road traffic offences involving a company car during 2011 and 2012 were quashed, the probe found. Almost half were not pursued.
The investigation showed one company had more than 200 unresolved summons issued against it.
By Brian Hutton