Four vehicles have been seized as a result of non-payment of tolls on the M50 motorway in Dublin since the introduction of barrier free tolling in 2008.

The National Roads Authority said it is chasing an estimated €4m in unpaid M50 tolls for 2013.

The figure represents 4% of the estimated total revenue generated from tolls.

The NRA has issued its annual reminder of enforcement procedures for non-payment of tolls.

It urged motorists who have outstanding tolls to make contact with M50 toll operator eFlow to settle their accounts.

The authority said over 30,000 civil summonses have been issued to toll evaders, with over 12,500 judgments being handed down in the courts.

It said 1,200 judgements have been passed onto the sheriff for collection.

The sheriff actions in these cases include formal collection of monies due and seizure of the vehicles.

Of the four vehicles seized, one was seized in Ballybrack in Dublin on foot of a court order of €5,624 for non-payment of tolls.

The money was paid, including costs to retrieve the car.

Two of the vehicles seized were eventually sold at auction.

A spokesperson for the NRA said the majority of penalty issues were resolved before it came to taking a vehicle and that it was never too late to make contact with eFlow to discuss payments.

The spokesperson said it could have an impact on someone's credit rating if judgment was taken up against them or their case was referred to the sheriff.

Around 110,000 trips are made per day through the M50 toll, generating about €100m a year in tolls.

The NRA said about 4% of vehicles passing through the toll do not pay.

Of these, half of the vehicles are based in the Republic of Ireland, while a quarter are from Northern Ireland.

The remainder are from other countries.

The NRA employs Euro Parking Collection to issue non-payment notices and collect M50 tolls from drivers in other countries.

A NRA spokesperson said its figures showed that the tolls collected in other countries pay for the expenditure of retrieval.