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.

03 April 2010

Emissions and metrication... (and apologies)

Dear all,

I am sorry I've been inactive with this blog for a while. I am currently studying a few months in Spain, so I've been in the "metric" world. However I went back home last week for a few days, and realised something rather interesting ...

---Start post---



Anyone looking at a car advertisement would be able to notice that emissions are never given in imperial units. It's solely given in gram(me)s per kilometre (g/km).

Now we know that this presents a problem, if:

a) road signs are in miles
b) fuel consumption is in miles per gallon [or even L/100km]

Why?

for example you're driving in a car with emissions of 100 g/km, for a distance of 385 miles.. how much CO<2 will be emitted?

100g * (385*1.6)km = 61600 g (61.6 kg) . This is still an approximate figure, because I rounded down the conversion factor between miles and km.

now if the distance were in km, look at the accuracy and precision.
100 g/km for a distance of 620km (same distance), we get
100 * 620 = 62000 g (62 kg) of CO<2.

If people are so concerned about meeting emissions targets and the like, why not make it easier to accurately calculate ones emissions?

You could use ounces per mile of CO<2, to be in accordance with the current system of miles on the road, but of course ounces are impossible to work with for anything that is scientific.

Hence the best solution to this would be to implement metric distance signs, and do something useful with the signs in miles, like recycle them as paperclips.