The air ambulance service in England and Wales flies 19,000 missions a year
Four or five times a day, anyone near the Royal London Hospital in the capital's East End can hear the familiar clatter of a helicopter taking off from the roof of the Accident and Emergency wing.
On board is likely to be Dr Gareth Davies, a consultant in emergency medicine and pre-hospital care. Along with a paramedic, another doctor and two pilots, London's distinctive red air ambulance will be flying to the scene of a serious accident.
This could typically be someone who's fallen from a height, a child with serious burns, or even the victim of a shooting. Mostly however, it is to attend a serious road crash.
Dr Gareth Davies flies to many serious road crashes
"Road traffic accidents are about 50% of our work," he says. "For the most part, these are pedestrians versus cars, the second most common being cars versus cars or cars versus lorries. Sadly it's a big proportion of our work load."
These are frequently life-threatening incidents, particularly when car occupants are trapped inside their vehicles.
"Even with vehicles travelling quite slowly, in the urban environment it is very common to see serious injuries to the chest, head, abdomen and pelvis," he says.
This often comes as a terrible shock to those involved in such incidents. In today's cars, it's not uncommon to feel invincible, or "car-cooned" as one expert has called it.
Cars are quiet and soundproofed against external noise. We feel reassured that the car has seatbelts, airbags, safety zones and such technologies as electronic stability control and ABS brakes.
However, the forces involved in an impact are tremendous as can be seen in any of the videos of cars being crash tested by Euro NCAP, the European car safety agency.
"If you drive into a brick wall at 30mph or two cars hit each other at 30mph, that's equivalent to falling from a height of 10m (30 feet), a third story window," explains road safety professor Murray Mackay.
"In that sort of standard crash, you go from 30mph to zero in a matter of inches (centimetres). Even if you're wearing a seat belt and everything goes according to plan, you're feeling a force 30 times gravity," he adds.
THREE CRASHES IN ONE
In a typical car collision, there are three crashes, the last of which causes most of the damage.
The first crash is the vehicle hitting another vehicle or solid object such as a tree or lamp post
The second crash is the occupant hitting the steering wheel or other part of the car interior
The third crash is the body's internal organs suddenly decelerating and hitting the inside of the chest, rupturing vital organs or blood vessels
The most serious injuries typically occur in side impact crashes. In frontal impacts the driver and passengers are protected by crumple zones, seat belts and airbags.
In a side impact, particularly one with a lamp post or tree, there is a lot less protection. In many cars, the only thing between vulnerable areas such as the head and any hard object is the side window and this typically shatters on impact.
"As soon as occupants are struck by the vehicle hitting them, or the tree they have run into, there are literally micro seconds before that occupant impacts with the tree or vehicle hitting their head, chest, or their pelvis," Davies says.
Even more horrifying, the chances of being ejected from the vehicle are also higher, especially if the occupant isn't wearing a seat belt, he adds.
That sudden deceleration imposes enormous strain on your body, says Dr Davies.
In any road crash there are three 'crashes', he explains.
First, you have the vehicle hitting another vehicle or solid object such as a tree or piece of street furniture. Then, the occupant hits the steering wheel or other internal part of the car. But it is the third accident that does the damage.
"This is where the internal organs of the body move forward and decelerate, hitting the inside of the chest, rupturing lungs, perhaps damaging the heart, rupturing the stomach or liver, and it's that third crash that causes the injuries or morbidity," he says.
It's why the air ambulance service is of such importance. It was created in the 1980s over concerns that too many people were dying at the scene of a road crash because it took so long to reach them.
This is the last in our current series of articles on road crashes in Britain. We are interested in your feedback and what you made of the coverage of this issue.
There are now 32 air ambulance services in England and Wales flying 19,000 missions a year, 40% of them to road traffic collisions.
In effect, the air ambulance brings the highly skilled doctors and the latest portable medical equipment to the roadside.
"For many people involved in a road crash, they are trapped perhaps by the vehicle, under the vehicle, or within the vehicle," Davies explains.
"Obviously their injuries continue to deteriorate all the time so it really is important to take as much of the hospital to the scene of the accident and to give patients who are in the process of dying the treatment they need to try and reverse that process as soon as possible."
Sadly many involved in road crashes die at the scene. Research indicates that 70% of road crash fatalities are declared dead at the crash site. The figure is higher for children.
A similar percentage of multiple serious injuries, known as 'polytrauma' cases are inflicted in road traffic collisions. As such, according to the Trauma Audit and Research Network at Manchester University, road trauma is the major cause of death and disability in the young.