How Sheppey avoided loss of life
The Sheppey Crossing pile-up involved 130 vehicles colliding in thick fog at high speed. Even worse, the crash took place on a bridge with no hard shoulder. Some commentators have said it was a miracle that no-one died.
Some witnesses said the pile up went on for 10 minutes and that cars were heading into the crash zone at 60-70mph.
At least 60 people were injured, of whom 35 required hospital treatment. Eight of them were seriously injured. But amazingly no-one was killed.
The vehicles were travelling fast. The speed limit was 70mph for this dual carriageway bridge, higher even than bridges that are wider. The Dartford Crossing is four lanes rather than dual carriageway yet the speed limit is only 50mph.
Previous incidents in the fog involving multiple vehicles have led to fatalities.
In 1991 10 people were killed after 51 vehicles crashed into each on the eastbound carriageway of the M4.
Three people died in 1997 after a 160 car pile-up on the M42 at Bromsgrove.
In 1984, nine people died after 26 vehicles collided on the M25 near Clacket Lane.
All these accidents occurred in fog. And in 2011 seven people died in a crash on the M5 after smoke from a fireworks display caused poor visibility on the motorway.
After the Sheppey accident, Kent Police's Assistant Chief Constable Rob Price said it was "a miracle" there were no life-threatening injuries. It is too early to say how no-one died, a police spokesman says.
One of the key factors in fatalities is whether there are heavy goods vehicles (HGV) that cannot stop in time, says Edmund King, president of the AA. After the Bromsgrove crash an HGV driver was convicted of dangerous driving. The sheer weight of a 44-tonne truck gives car passengers little chance when hit at speed.
"When you look at the M42 crash, the thing that killed people was the HGV ploughing into the back of vehicles and basically crushing them," says King.
A Kent Police spokesman says that two car transporters - one empty - and two HGVs are thought to have been involved in the collision.
From the pictures, it appears they were able to stop without causing too much damage, says King. "The miracle is that there wasn't an HGV ploughing into the back of everyone [at high speed]."
It has been reported that a quick-thinking lorry driver blocked the approach to the bridge to prevent any more cars from entering the crash zone.
The second crucial factor is how much safer cars are today as opposed to 10 or 15 years ago.
The EuroNCAP (new car assessment programme) system - better known as the star safety ratings - has put the onus on manufacturers to improve car safety beyond minimum standards.
Motoring journalist Quentin Willson thinks the word miracle is unnecessary. For him it's all about the design. "In the old days if you'd been in a Cortina you would have gone through the windscreen. The engine would have folded." Nowadays the chassis is much tougher and this is unlikely to happen, he says.
There has been a 50% reduction in death and serious injury for car passengers over the past decade, says Matthew Avery, head of research at Thatcham, the research body that tests cars for the EuroNCAP star ratings.
"There are two ways of getting killed in a crash - you can get crushed or have forces exerted on the body that are too great to bear," he says.
Car manufacturers have improved safety features in relation to this. A safety cage now envelopes the cabin, stopping passengers from being crushed. There are crushable zones around it to take away the energy from the crash.
Previously, drivers would be at risk of having their legs or feet crushed as the cabin would give way and pedals come towards the driver, Avery says. Today that shouldn't happen as the interior will remain intact.
Seatbelts have load limiters, which give a little, thus reducing the forces on the body at high speed braking.
There are more airbags. Side airbags protect the thorax and body. Curtain airbags fill the space where the window is and protect the head. Head restraints go forward to help protect against whiplash.
The bridge was probably a contributory factor, increasing the scale of the pile-up, King says. Cars coming up to the apex may not have been able to see the density of the fog on the other side.
But the central reservation and side barriers on the bridge "did their job" King says. They prevented vehicles from plunging off the side or into oncoming traffic on the opposite carriageway.
In the future, the scale of multiple-vehicle pile ups will be radically cut by technology, Avery believes. At present only 1 or 2% of cars have AEB (autonomous emergency braking) - where the car brakes automatically or warns the driver at the sign of an obstacle ahead.
"It's radar-based so that even when it's foggy it would have worked," he says. And soon it is likely to become a common feature.
Next year cars seeking a five-star safety rating will require AEB features. Also from 2014 it will become mandatory for lorries to be equipped with forward collision warnings. Crashes will still happen but there will be very few big pile-ups, Avery predicts.
"Things like the Isle of Sheppey crash just won't happen in 10 years' time," he says.