Watch John Ryall's report below
Almost a million pounds worth of fines issued at the Dartford Crossing were avoided by lorry drivers from abroad last year.
More than 150,000 trucks registered abroad failed to pay the £6 charge, resulting in a penalty notice.
The Freight Transport Association says foreign vehicles are getting away without paying the fines because they're harder to track down.
It's quite difficult actually to follow up on non-UK registered vehicles in comparison to those that are registered here in the UK with DVLA. But there are ways which it can be done and there are enforcement agencies across Europe that can be used and we just think that more efforts need to be made to make sure that those that do use the crossing actually pay." >
The toll booths were taken down four years ago and replaced by a free-flow toll payment system based on the automatic recognition of vehicle number plates.
Failure to pay the toll triggers a fine.
Highways England say 80% of foreign truckers pay the Dart Charge compared with 95% of UK-based lorries.
Elsewhere in the UK, tolls are fast being abolished.