18 April 2010

DfT Traffic Signs Manuals Chapter 4 : use of metres and miles per hour

Whilst reading through the Department for Transport's Traffic Signs manual (chapter 4), I came across something rather striking. Striking, as in the fact that stopping distances are in metres, with speeds in miles per hour. Now the reason why this is striking, isn't because I've not seen this before. Everyone who has read the Highway code would already have seen the muddled miles per hour - metres stopping distance many - a - time.

However, I came to realise how difficult it must be to calculate stopping distances in miles per hour, since mathematically, deceleration is done in metres per second squared, hence to calculate the stopping distance, miles per hour will have to converted to metres per second. 1 m/s = 2.23693629 mph [compare with 1 m/s =3.6 km/h]


I won't bore you with more mathematical calculations, as I've seemed to be doing a lot of recently, but, I'm sure the stopping distances shown in the DfT's manual (and the highway Code) are somewhat wrong. The only way to fix this, for the sake of accuracy would be to move towards km/h and eliminate miles and all its forms.

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