The absurdity of the use of kph

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  First and foremost I apologise (yet again) for such a long gap in between blog posts. The return of freedom over the past year has kept me away from screens. They say it takes 66 days to develop a new habit. Running is a habit I developed over lockdown, but the return to the office (and I intend to never work from home again) and frequenting the pub has reduced frequency of this.  It is, however, not completely bleak for my physical well-being. Cramming a number of social events in after work has led to me doing a lot more walking around central London. I don’t have an Apple Watch, (other brands of smart watch exist), but my iPhone records my steps and a lot of really interesting data on my walking and running. As would be no surprise, I’ve configured everything in metric units. Thankfully, gone are the days where Apple would dictate to you , based on your location, the units of measurement you use. You have a chose whether to specify distances in miles or kilometres....
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DfT Traffic Signs Manuals Chapter 4 : use of metres and miles per hour

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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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