Taxis with loose steering wheels or totally bald tyres. Mini buses with no insurance or licences to operate. Cars that are so dangerous they have to be taken off the road immediately.
These were all discovered in a random swoop by the Driver and Vehicle Agency in and around the city of Londonderry in just one night, and BBC Northern Ireland's environment correspondent Mike McKimm was with them.
Working on a tip-off that illegal mini buses were operating in the area, the team set up road blocks and soon caught some of the miscreant vehicles.
The first vehicle was totally unlicensed, yet was carrying passengers at the time it was stopped. So it was impounded by the agency.
"We have fare-paying passengers on board," said Stephen Spratt, DVA operations enforcement manager.
"These people may not be properly insured in the event that the vehicle is involved in an accident."
And it wasn't much better news with some of the taxis that were stopped.
One taxi stopped had little that was right with it.
"There's no valid taxi plates on it," explains Mr Spratt.
"Checks have brought into question whether there is valid insurance on it.
"And in addition to that it has a tyre that is practically worn smooth.
"Ultimately we are talking about the public paying to travel in this type of vehicle, so you can see the benefit of the work that we do in taking this sort of vehicle off the road."
Just when it seems it couldn't get any worse for the driver of the taxi, it was discovered to be running on illegal green diesel.
This low-duty fuel is only available in the Irish Republic for use in agricultural machinery. The car wasn't going any further.
The problem was that this was a pattern repeated again and again, taxi after taxi. That night, not one taxi checked would be free of defects.
"Come and see this," offered one enthusiastic DVA man.
As I approached another taxi with its door lying open, he moved the steering wheel up and down - not from side to side.
It wobbled about and was quite clearly quite loose.
I was told that the driver admitted to the fault but claimed it was "OK to drive".
The list was endless. As car after car was examined it became very apparent that all was not well.
Almost all the vehicles were stopped at random, yet all the taxis were found to be defective and were forced off the road.
Boy racers in their lowered cars didn't fare any better.
Every modified car examined was forced off the road.
One was found to have a broken suspension after its springs had been cut in half to lower it, as well as faulty brakes and tyres that were rubbing against the body shell.
One of its front wheels was all but hanging off.
Often the suspension systems of these cars collapse, sometimes with fatal consequences.
Perhaps most worrying was the number of buses found to be faulty.
Forty per cent of those stopped were defective and a third were forced off the road. Some were highly illegal, with at least two drivers facing a day in court.
All of this happened in just a few hours in less than a square mile of Derry City.
Some say that as the Christmas festive rush gets under way, the demand for taxis and mini buses could bring out even more of these deadly vehicles to be used and paid for by unsuspecting passengers.