Longer vehicle checks at the Eurotunnel after Brexit could leave drivers stranded in motorway tailbacks for as long as five hours, a new study suggests.
Checks at the currently free-flowing border could spark tailbacks as long as 30 miles, research from by Imperial College London showed.
The study, commissioned by the BBC’s Inside Out South East, showed that current vehicle checks at Folkstone last on average two minutes.
Drivers travelling within the EU do not complete customs checks and undergo basic vehicle searches.
Drivers on the M20 are already forced to wait as long as 2 hours during peak times between 4pm and 5pm.
Dr Ke Han, assistant professor of transport at the university, found that for every two minute check traffic jams increase as much as 10 miles.
If extra checks lasting an additional two minutes are imposed motorists heading for Dover may be forced to queue for a combined 29.3 miles.
Traffic could run from the entrance of the Channel Tunnel at Folkstone to near Maidstone and in the opposite direction towards Dover.
Drivers travelling between Maidstone and Dover could be forced to wait as long as five hours for a journey supposed to take as little as 50 minutes.
Dr Ke Han told the BBC: “What’s shocking is the check time applied to each individual vehicle could lead to tens of miles of delays of hours of queueing on the motorway.”
Researchers studied data including traffic simulations for the area, using data from official sources such as Highways England, the Department for Transport, the Port of Dover and maps.
The research also accounted for different kinds of vehicles such as passenger vehicles, light goods vehicles, heavy goods vehicles (HGVs) and coaches.
The university said it was not yet clear what part of the departure process contributed to check times, both now and in the future.
The university said more research was planned, but added that the outcome of Brexit negotiations was still uncertain.
A spokesman for the Treasury told the BBC that the government wanted a customs arrangement that ensured trade with the EU was as frictionless as possible.
He said: "We set out our two preferred models in our Customs White Paper, but, of course, the final arrangements will depend on the negotiations with the EU."