Tag Archives: Breaking

Stopping Distances for Driving Test

Brake Lights Stopping

Brake Lights Stopping

This post includes a little tip I read somewhere, but I can’t for the life of me remember where. I read so much stuff before I did my theory test. In my opinion stopping distances are kinda useless, since you can’t really calculate them on the fly, but you still need to know them. Its more a visual or spacial awareness thing while driving.

You know *your car* need “this” much space to stop and thats kind of it.

I mean without any extensive thought, some of the variables are Road Condition:  Wet / Dry, Weather: Hot / Cold, Humidity: Dry / Wet, Tyres: Slick / Knobbly / Worn, Road Material: Loose / Firm / Soft, Tyre Pressure: Over Inflated / Under Inflated / Correct, Brake Type:  Disk / Drum, Brake Material: Steel / Carbon / Ceramic, this before we get to Electronic / Mechanical like ABS, Stability Control and Brake Assist and without too much thought, the variables must be into millions of permutations.

Stopping Distances by DVLA

Stopping Distances by DVLA

All these are dependent on when the driver actually realises they need to stop, and their reactions and indeed actions. 

However you need to know these for your theory test and I guess for your actual driving test because of the Show Me, Tell Me Section and / or when the examiner asks you questions during the independent driving portion.

Top Tip: Easy Braking Distance Calculation

There is an easy way to calculate these, its quick and easy. Which makes me equally proud of the mathematics but also suspect about authenticity of the figures. Not to mention if they actually have any real world correlation or basis.

You basically multiply the speed by using an incrementing modifier, so for example..

The Overall Stopping distance in feet:

Speed (MPH)  Qualifier (Feet)  Multiplier Distance (Feet) 
20 mph 20 ft 2x 40 ft
30 mph 30 ft 2.5x 75 ft
40 mph 40 ft 3x 120 ft
50 mph 50 ft 3.5x 175 ft
60 mph 60 ft 4x 240 ft
70 mph 70 ft 4.5x 315 ft
100 mph 100 ft 6x 600 ft
160 mph 160 ft 9x 1140 ft

 

You maybe thinking, but I need to know meters not feet. Negative, the theory test gives you the distances in both feet and meters. 

The Fastest Travelling Speed

This got me thinking about the fastest speed I have travelled, which were 155mph in a car with a NOS kit, along the lines of what the Wizards of NOS do, obviously not driver. We were in moist conditions on a slight down gradient and talking with music on, which can slow reaction times…

Lowes Motor Speedway Quater Mile Marker

Lowes Motor Speedway Quater Mile Marker via Wikipedia.

155mph slightly distracted by music and chatter giving slower than average reaction times, on moist/damp conditions makes the stopping distance 3,135 ft / 956 meters. 

The Earths curvature means at absolute best a 6 ft man can see between 1.8 km and 5 km away through a telescope or binoculars before the Earths curve obstructs your view. Whether your eyes could see anything smaller than a bus at a distance of 956 meters is debatable.

The above image is taken at around 500 meters / 1,600 feet from the building. I don’t think you’d be able to see the child and their father on the left from double this at 1,000 meters. Assuming you could even see them, my guess it they would be road kill at anything over 80 mph, at 158 mph, the driver and passengers would need to be steam cleaned off the buildings wall.

155mph = 70 meters per second.

That building is approx 6-7 seconds away at that speed and about 13 seconds away with the breaks on. Not even a Bugatti Veyron would be able to able to stop in time and that has some of the best brakes and air breaks in the world. 

This isn’t really an anti-speeding post, its more an awareness post, 1,000 meters or over half a mile sounds like a long distance, but when you think, at 70mph its 30 seconds away. 

 

Brake Lights Image by Myles Davidson.

A Manchester Based Photographer and Website Developer with interests in Strongman, Fitness and Geekery.