Potholes and poor roads are being blamed for high failure rates at some NCT centres.
A third of centres across the country have more cars fail than pass on their first go.
In one centre - Derrybeg in Donegal - 10% of vehicles failed for "dangerous faults", more than twice the national average.
Castlerea in County Roscommon has the lowest pass rate in the country.
Transport commentator Conor Faughnan says getting your car passed can depend on where you live:
"If you look at counties like Donegal, Kerry and Mayo - counties that have a lot of road.
"Cars that use those roads regularly are hitting potholes much more regularly than city dwellers and that actually shows up in the NCT stats.
"When you throw your car into the NCT for your honest diagnostics the NCT is able to tell you your headlights are misaligned, and that more likely happened to you in Donegal than Dublin."