There has been a lot of talk by the UK government regarding increasing the National Speed Limit on Motorways to 80mph.

The only outcome in allowing this to happen will be more road incidents involving death or serious injury and a massive increase in fuel spend. The table below illustrates time saved per mile as driving speed is increased.

MPH Feet/Sec
Travelling Distance
Miles Covered
in Mins
Miles Covered
in Sec
Time Saved
(per mile)
10 14.67 6 0
20 29.33 3 0
30 44 2 0
40 58.67 1 30
50 73.33 1 12
60 88 1 0
70 102.67 0 51 9 sec
80 117.33 0 45 6 sec
90 132 0 40 5 sec
100 146.67 0 36 4 sec

  • Fuel consumption will increase by 20-25% when speed increases from 70-80mph
  • Stopping distance at 80mph will be 400ft (an increase of 85ft from 70mph)
    (see article on stopping distances and kinetic energy at https://www.riodrivingschool.co.uk/stopping-distances-and-kinetic-energy/)
  • you only save yourself 6 seconds per mile!

The obvious answer to the title of this article is NO!  80mph makes no sense at all.

Any rational person would agree that it’s not worth burning 25% extra fuel for a saving of just 6 seconds.  That said, we quite sure there will be many ignorant drivers who will lawfully drive to 80mph and then beyond.

Saving More Time

You simply don’t save that much time by increasing your speed to 80 mph. If you drive the entire 400 mile distance from London to Edinburgh, you would only save 40 minutes, and that assumes that you maintain a constant speed of 80 mph the entire time, neither accelerating or decelerating.

70-80mph

Kinetic Energy and Stopping Distance

Kinetic energy and stopping distances

The kinetic energy of a vehicle is what makes it dangerous; transferring that kinetic energy to an object – be it a pedestrian or another car – is what causes damage. Kinetic energy depends on the square of the speed; if you double the speed of an object you quadruple its kinetic energy. An increase in speed from 70 mph to 80 mph is a 14% increase in speed but this results in a 31% increase in kinetic energy, making the car – in a sense – 31% more dangerous to other road users.

Increasing kinetic energy also increases stopping distance. Increasing the speed limit to 80 mph would increase the average stopping distance on motorways to 120 metres (30 car lengths!), a 25% increase on the 96 metre stopping distance found at 70 mph.

Fuel Economy

The relationship between speed and fuel economy is not linear; fuel economy is poor at both low and high speeds and peaks somewhere between 40 and 60 mph. Driving at 80 mph will decrease fuel economy and therefore increase fuel consumption; fuel costs will be higher and CO2 (and other harmful gas) output will be higher. Our limited supply of fuel will be depleted faster if we all drive at 80 mph than if we drive at 70 mph.

Force of Impact

These factors will affect vehicle handling:

  1. Inertia. The law of inertia, also known as Newton’s first law of motion, says that an object will remain at rest or in motion in the same state unless acted upon by some outside force.
  2. Kinetic Energy. Referred to above as energy of motion, this is the energy that an object, such as your vehicle, has when it moves.
  3. Centrifugal Force. This is the force that pushes a vehicle away from the centre of the road in a curve.
  4. Gravity. This is the force that draws objects to earth. Gravity affects uphill and downhill motions.

The faster you drive, the less time you have to react to hazards in the road around you.

Every time you increase one of these factors, you also increase the force at which you will hit an object. An increased force of impact also means an increased risk of injury or death in a collision. When you increase any of these factors, the result is:

  • An increase in stopping distance.
  • A reduction in vehicle control.
  • An increase in the force of impact.

These factors affect the force of impact:

  1. The speed at which you travel. When you increase the speed of your vehicle, you also increase the force of impact when you hit an object.
  2. The total weight of the vehicle, including passengers and cargo. When you increase the weight of an object (such as your vehicle or the object you are about to hit), you increase the force of impact.
  3. The distance your vehicle has to travel between the time you apply the brakes and impact. When the distance you travel before you stop increases, you increase the time you have to slow down before impact, thereby decreasing the force of impact. This decrease in the force of impact also decreases your risk of injury or death in a collision.

An increase in speed and weight will:

  • Increase your vehicle’s stopping distance.
  • Reduce your control of the vehicle.
  • Increase the force of impact.

Let’s understand what happens to you and your vehicle during the 1st second of impact

1 second and you’re dead!

The First Second of Impact

A crash can take place in a matter of seconds. Some experts determined that the following would happen to a driver if a vehicle traveling at 55 mph were to crash into a fixed object, in the first second of impact:

  1. First tenth of a second: The front bumper and grill collapse.
  2. Second tenth of a second: The hood scrunches up, rising and striking the windshield. The rear wheels, still spinning, lift from the ground. The wheel arches begin wrapping themselves around the object. The car’s frame stops, but the driver and the rest of the car is still going 55 miles an hour. Instinct causes the driver to stiffen his legs against the crash, and they snap at the knee joint.
  3. Third tenth of a second: the steering wheel starts to disintegrate, with the steering column pointing straight at the driver’s chest.
  4. Fourth tenth of a second: The front two feet of the vehicle is wrecked, while the rear end still moves at 35 miles per hour. The driver’s body is still traveling at 55 miles per hour.
  5. Fifth tenth of a second: The steering column punctures the driver’s chest, and blood rushes into his lungs.
  6. Sixth tenth of a second: The driver’s shoes, despite being tightly laced, are ripped off his feet. The brake pedal breaks off. The car frame buckles in the middle. The driver’s head smashes into the windshield. The rear wheels, still spinning, fall back to earth.
  7. Seventh tenth of a second: Hinges rip loose, doors fly open and the seats break free, striking the driver from behind. At this time, the driver is already dead.

The above assumes these two things: the vehicle has no airbags (or they failed to activate), and the driver did not wear a seat-belt. If that driver had been properly secured by a seat belt, he would not be hurtling toward the steering column at dangerously high speeds and thus remain potentially safe.

The crumple zone collapses upon impact, cushioning the passenger compartment.

Energy-Absorbing Features
You may not know it, but there are more safety features in a vehicle than just seat belts and airbags. Several vehicle components must be designed to meet safety standards. Vehicle safety features that absorb the energy from a crash include:
  • Crumple zones (the front and rear crash areas).
  • Energy-absorbing bumpers.
  • Side door beams.
  • Reinforced windshield (windshields are specifically designed to reinforce the roof so it does not collapse).
  • Padded dashboard.
  • Head restraints.
  • Airbags.
  • Safety belts.
  • Antilock brakes.

The crumple zone collapses upon impact, increasing the vehicle’s stopping distance and cushioning the passenger compartment by absorbing the energy. Windshields keep you protected inside your vehicle. Seat belts keep you from being thrown around inside the vehicle, as well as from being ejected. Frontal airbags keep you from hitting the dashboard, and side airbags keep you protected from the sides. Head restraints keep your head from snapping back. These are just a few of the many design features in your vehicle that help to decrease the force of impact and increase your control over the vehicle as well as the vehicle’s performance. The decreased force of impact works as a cushion that protects you in a collision.

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