A watchdog report today questioned the reliability of driving tests in Northern Ireland and voiced fears about thousands of unfit learners obtaining passes on an annual basis.
The study found that the pass rate here dropped by 12% when the test examiner was accompanied by a supervisor.
And it called for urgent investigations into the discrepancy, given the particularly poor road safety record of young drivers in the province.
The report was compiled by the Northern Ireland Audit Office and will form the basis of a major inquiry later this year by the Stormont Assembly's Public Accounts Committee.
It examined "notable progress" made since the authorities launched a new road safety strategy in 2002.
But it pointed out that the rate of deaths and serious injuries on the roads remains higher than in the rest of the UK.
The Audit Office, the province's Government spending watchdog, said young and inexperienced drivers continue to be "disproportionately represented " among the statistics.
In 2005, the 16-24 age group accounted for 27% of all traffic accidents involving death or serious injury - despite comprising only 13% of the population.
It called for the official road safety strategy to include a specific target for reducing the carnage among young drivers.
It also voiced concern at driving test figures for the period April 2004 to January 2006. These showed that the overall pass rate of 47% dropped to 35% when the examiner was being supervised.
The Audit Office said this 12% gap was more than double the margin of error of 5%.
It commented: "We estimate that the current 12% differential creates the potential for over 5,000 candidates to pass the test annually without meeting the required standards.
"Given the poor safety record of young and novice drivers, such an outcome is likely to have had a adverse effect on Northern Ireland's road safety record.
"As a full driving licence can only be revoked on health grounds or following enforcement activity, any shortcomings in the assessment of driving tests has the potential to impact negatively for the future.
"Based on 2004 statistics, there are 0.19 deaths, 1.5 serious injuries and 10.4 slight injuries for every 1,000 drivers on Northern Ireland roads.
"In respect of the 5,000 drivers this potentially equates to an additional one death, eight serious injuries and 52 slight injuries annually and a total cost of £3.25m to the economy."
The report urged the Government's Driver and Vehicle Agency to investigate the reasons for the different pass rates and take "the necessary remedial action".
It also noted that the GB-based Driving Standards Agency had highlighted the issue in the 1990s.
The Audit Office pressed the Department of the Environment to proceed with delayed plans for a review of the 45mph speed limit for 'L' and 'R' drivers after cameras at two major Belfast traffic routes recorded a speeding 'R' driver passing every two minutes.