Roads leading to the county's Channel ports could become "impassable" during peak holiday periods next year thanks to stricter EU border rules.
The introduction of the new Entry/Exit System (EES) will require non-EU passengers to have fingerprints scanned and a photograph taken when they pass through the Eurotunnel terminal at Folkestone and the ferry port at Dover.
Transport chiefs have warned that the new rules - applicable to 'third country' UK nationals following Brexit - could cause chaos on routes leading to the border as checks will take longer and there is not space to easily manage people having to get out of their vehicles to provide biometric data.
Agreement between London and Paris means that border checks for entry into France, where EES applies, are carried out on the British side of the Channel.
"Any disruption to the French inbound control has an immediate knock-on effect on traffic in minutes," Eurotunnel director of public affairs, John Keefe, told the House of Lords Justice and Home Affairs Committee yesterday.
Mr Keefe explained that in the summer peak for tourist travel as many 1,700 passengers per hour would need to have their EES status approved and processed for the first time - a task he described as "impossible" in the space available at the terminal at Cheriton.
"The risk of congestion is to our motorways," he told the committee's hearing. "Once all of those areas are congested, Kent becomes impassable.
Tim Reardon gives evidence to the Lords committee
"Managing passenger vehicles, individual consumers, when they have an imperative, ‘we must get there’, is a completely different kettle of fish.
"They disobey rules quite happily, and will leave the motorway and will look for alternative routes which they’ll then congest, and we’ll very quickly have a very widespread issue in Kent."
Although no firm date for introducing the new system - which the the EU says will "safeguard and increase the security of the Schengen area" - has yet been given, it is expected it could be in place before the summer holidays.
Tim Reardon, head of EU exit at Dover Harbour Board, explained to the committee how applying these tightened border checks at the Port of Dover is far more difficult than at airports.
"In our context, almost everybody is in a vehicle and there is no way yet of doing a biometric control on a vehicle without getting everyone out of the vehicle," he said.
"That’s the one thing on our site which cannot happen because you’re in the middle of live traffic. It would be equivalent to asking people to get out of their car at a motorway toll booth. It’s fundamentally unsafe and it can’t happen.
"So the challenge is to find a way of squaring that circle and matching those two incompatible concepts."
Holidaymakers hoping to get away during the October half-term had a taste of the potential disruption to come when they had to wait up to 10 hours on the M20 after power supply problems hit services through the Channel Tunnel.
Some families decided to turn around after being stuck in traffic near Folkestone, while one person, who did make it onto a Eurotunnel train, described the situation as "absolute carnage".
Last Christmas the Army had to be called in to help deal with a huge backlog of trucks stranded in Kent following a decision by the French authorities to shut their border amid the spread of the 'Kent variant' of the coronavirus.