The operators of the barrier-free tolling system on the M50 say that around 1,900 motorists a month are tailgating to try to avoid paying their toll.

Eflow says that in many cases motorists are travelling just 1.2 metres behind the vehicle in front of them and have described the behaviour as frightening.

More than 100 motorists have been issued with fines and penalty points following a number of Garda operations to tackle the problem.

Gardaí say they are continuing to watch out for this behaviour.

Eflow has installed rear facing cameras on the motorway to catch those who are tailgating and to discourage this kind of driving.