The scale of Northern Ireland's appalling road safety record was exposed today, amid fears that 5,000 learners are wrongly passing their driving tests every year.
A watchdog report also estimated that up to 42,000 speeding motorists escaped detection here in a 12-month period, due to a policing administration shortfall.
The Northern Ireland Audit Office study revealed that driving test pass rates slumped by 12% when examiners were overseen by a supervisor.
It called for investigations into this disparity and said it created " the potential for over 5,000 candidates to pass the test annually without meeting the required standards".
Today's report said "insufficient capacity" within the PSNI's fixed penalty processing centre had hit the enforcement of speed limits. This deficit has affected the thresholds above speed limits at which fixed notices or summonses are issued.
The Audit Office did not disclose these speed tolerance levels in Northern Ireland, but revealed that they are higher than the levels recommended by the Association of Chief Police Officers (ACPO) in Great Britain.
"Although PSNI has not estimated the number of offenders escaping prosecution because of its inability to comply with ACPO guidelines, detections increased by between 66% and 200% on two occasions in 2003 and 2004 when it temporarily lowered the settings on the four Belfast cameras, compared with the corresponding period in the previous year," the report said.
"During 2005, we estimate that between 32,000 and 42,000 NI motorists may have escaped possible detection for speeding.
"In addition to the potential negative impact on road safety, this also means that potential revenue of between £1.9m and £2.5m was lost in that year."
The Audit Office estimated that road deaths and injuries cost the Northern Ireland economy £451m in 2005.
The number of fatalities here per 1,000 people that year stood at 7.9, compared to 5.5 in Great Britain.
The proportion of drink and drug-related fatal collisions was 17.3% in the province and 11.1% across the water.
Drink-driving detections by the PSNI are increasing but fewer than 2.5% of drivers are being screened annually for alcohol and drugs, the Audit Office said. European experts have recommended a figure of at least 10% and up to 25%, if feasible.
Today's study said the available evidence suggested that Northern Ireland was lagging significantly behind GB on speed camera coverage.
PSNI plans to increase speed camera numbers here were held up between 2003 and 2006 due to a delay in legislation and administrative problems.
Detections from the four Belfast fixed cameras slumped in 2005/06, meanwhile. This was partly due to technical snags that led to them being out of operation on a number of occasions.
The PSNI has stressed to the Audit Office that these difficulties have been completely resolved.
It has also stated that the issue of insufficient capacity in fixed penalty processing is common to all UK police forces.