Taxi drivers face spot checks over the coming weeks as part of a Hertfordshire-wide police crackdown.
Hertfordshire Constabulary has announced it is launching a series of operations to make sure taxis are safe for passengers.
Operation Vector will see hackney carriage and private hire vehicles randomly checked to make sure they are road worthy and officers will also be running background checks on drivers.
Police Sergeant Sam Cordingley, who is leading Operation Vector, said: "While we believe the vast majority of taxis and private hire vehicles operating in Hertfordshire are safe to use, it is important that if they fall below the required standards, then action is taken against them.
"We take this very seriously and any drivers found to be flouting the law or the terms of their licence, may find that their licence is suspended. This work is being done to ensure that the public can be confident that the taxis they get into provide a safe and secure means of transport around the county."
The operation began last week and has already seen five taxi licences suspended. Officers have handed out six notices for vehicles faults including a fuel leak, five defective tyres, two faulty batteries and one brake issue.
The operation has also uncovered one suspected fraud, which is now being looked into by benefits investigators.
PC James Wood, who led the operation last Friday, said: "This was a successful operation with a large number of taxis and drivers being checked on the night by police and the local licensing officers.
"Most of the vehicles were found to be safe and road legal, however a number were not and in those cases the licensee now has a short amount of time to fix the faults or face further action."
Police and Crime Commissioner David Lloyd added: "The public needs to know that when they get into a taxi in Hertfordshire, that the vehicle is maintained to the correct legal standard and that the driver is a safe person to travel with."