Concern about motorway congestion is now so serious, officials have drawn-up an emergency plan to deal with complete gridlock on the UK's roads, a BBC programme reveals.
Drivers could be evacuated from their cars in extreme gridlock
In the BBC's drama documentary The Day Britain Stopped, "Operation Gridlock" - an emergency plan reserved for catastrophic situations - is implemented after most of the UK's motorways grind to a halt in freezing conditions.
It seems an unlikely scenario, until you consider that it was only late January this year that hundreds of motorists were trapped in their cars overnight in freezing conditions on the M11.
But what is Operation Gridlock and would it have been implemented for real?
In fact, Operation Gridlock came into being because Surrey emergency planning officials wanted a formal plan to deal with emergencies in the face of ever-rising congestion on the M25 and other motorways.
Paramedics on motorcycles
The plan sets out how to deal with long-term gridlock and includes measures such as evacuating people from their cars, setting up emergency inflatable roadside shelters, distributing food and drink and having paramedics driving through jams on motorbikes attending to trapped motorists.
Chief Superintendent Bill Harding of Surrey Police Specialist Operations, says: "By 1999 we decided to formalise our arrangements with the other emergency services, the fire brigade, ambulance service and the county council, on how to deal with incidents.
"We wanted to make sure that everyone communicated with each other and that there were no gaps in our response."
The chief superintendent emphasises that the plan is not a rigid document; it is designed to ensure that all the relevant services communicate throughout any emergency and that key resources are readily in place if a situation worsens.
He says: "First of all our priority would be to get the traffic moving and to attend to people caught up, either directly or in stationary traffic behind, an accident.
"The commander at the scene would assess the situation, report back to central command, and if necessary ask that parts, or all, of Operation Gridlock be put into action.
"For example, we recently had a tanker carrying resin overturn on the M25. We were advised by the company experts that the resin was "low temperature impact", that is, it could ignite at low temperatures.
"All agencies decided to implement sections of Operation Gridlock, we closed one side of the motorway completely between Junctions 10 to 13 and reduced traffic to the two far lanes on the other side.
Parts of the plan are confidential
They also parked an ambulance near the accident scene which acted as a stationary medical assistance point and sent officers on motorcycles through the traffic to keep people informed and check if anyone needed medical assistance.
"You'd be amazed how many people do, such as pregnant women, diabetics and people who suffer from claustrophobia and anxiety attacks," says Harding.
"We have to allow for very serious medical emergencies and even have paramedics who are trained to deal with trauma in position to carry out operations actually at the scene."
So how bad would congestion need to get before the emergency plan was put into force?
"Had this accident combined with another big accident, it is likely we would have brought Operation Gridlock into action.
"For example, we recently had another lorry crash into and damage a bridge on the M25. With debris falling on the road and cracks appearing in the bridge from heat damage, we had to close the motorway.
"These two incidents combined would take a couple of days to resolve and we would certainly have put Operation Gridlock into action."
Harding also says that parts of the plan have to remain confidential, for example details of where emergency shelters would be sited, because individuals could sabotage any rescue efforts.
"We are always keen to release as much information as possible but we wouldn't divulge the details because someone, possibly a terrorist looking to disrupt the operation, could easily frustrate our plans," he says.
While Chief Superintendent acknowledges the scenario in The Day Britain Stopped could happen, he insists you would have to be very unlucky for all of those events to happen on the same day.
"But then, some time ago I attended an emergency training course and our scenario involved a passenger jet coming down on a residential area where there was a large non-English speaking immigrant population.
"In our pretend scenario, flats were demolished, there were hundreds of casualties and difficulties in locating residents or finding out who was missing because of language difficulties.
"At the time I thought it was fairly far-fetched, but then the very same thing happened four months later outside Amsterdam - so you never know."
The Day Britain Stopped was broadcast on BBC Two on Tuesday, 13 May, 2003 at 2100 BST.