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How steep is a 20% hill?

It doesn't matter exactly what it means, 20% is steeper than 10%. In surveying 20% is interpreted as 20% of a right angle (i.e. a brick wall) and so would be 18 degrees.

theguardian.com - When, and why, did British road signs warning of a steep hill change from ...

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THIS SCEPTRED ISLE

When, and why, did British road signs warning of a steep hill change from the perfectly understandable `1 in 5' to the quite meaningless `20%'? Jon Smele, Glasgow Renfrewshire Giving a date would be difficult but there are still many examples of the 1 in 5 type signs. I think it is an Engineer's logic to use percentages, but 20% isn't meaningless it just means 1 in 5. In any case the angle is just a rough and ready indication warning drivers to change a gear downwards and to be alert to a possible runaway. Jack Hill, St Albans England Don't know about the when but I think the why might be because of our compulsion to adopt American usages. Percentages have always been used to describe the "grade" of US railway tracks. Steve Barrett, Brgess Hill, UK From memory, it was the mid '70s and to fit in with the European system. Boo, Bacup, Lancashire 20% is not meaningless unless you are woefully un-numerate. Indeed, I think that, to most people, it has lot more meaning that '1 in 5', which requires you to understand that is shorthand for 1 unit in height for each unit in length. Percentages have the additional benefit that the number increases with the steepness of the hill, so aiding clarity. It is not immediately obvious to some that '1 in 3' is steeper than '1 in 5', but 33% is clearly more than 20%. Daniel Owen, London, UK Gradients of the form 'x in y' are more readily understood than the arithmetic abstraction z%. But there's nothing more woefully illiterate than to describe me as 'woefully unnumerate'. Pete Wigens, Stroud, Glos UK 'One in five' and '20%' mean exactly the same thing, but I have to think about it to picture whet they mean in terms of gradient. Why not just use degrees? Interestingly, here in New Zealand, nobody bothers to put up a sign saying how steep a road is. Unless they think it might be the steepest street in the world, in which case it's a matter of pride. caroline, wellington new zealand Pete Wigens, you grasped my point, which might have been made more clearly I suppose. Daniel Owen, you miss it: 20% of what? Yes, of course, both can be misinterpreted, but 1 in 5 is surely clearer? And where is the evidence that its previous usage had led to accidents? I guess what I wondered was how was it that some Ministry of Transport civil servant (although I guess they are now a Ministry of Customer Conveyance Operative or something)should decide on such a change and, more importantly, how it should be inflicted on all UK road users! Well, I guess I know the answer, actually: in 30 years of professional life I have seen no end of such fiddling with systems that are already more than appropriate, largely because you want to show a fearsome higher body that you are doing something and not sitting on your (more often than not) perfectly well thought out and excellently functioning laurels! Next they will be getting somebody to redesign that sign of the guy fighting with his umbrella that we all recognise as meaning `roadworks ahead'... Jo Smele, Glasgow Renfrewshire Jo Smele - 20% of 100% of course. Clearly you don't understand what a dimensionless percentage actually is if you believe it needs to be applied to some quantity. Jonathan Hobbs, Pease Pottage, UK Surely, a clearer way of indicating the gradient would be to simplify it to three main categories: a. Gentle b. Steep c. Bloody hell!!! Ian Markham, Sheffield UK 20% of what? writes someone. Of 100%, of course, with 100% being a brick wall which it seems most of you have hit. David Spedding, Torun, Poland Jack Hill probably has it right. It doesn't matter exactly what it means, 20% is steeper than 10%. In surveying 20% is interpreted as 20% of a right angle (i.e. a brick wall) and so would be 18 degrees. This is 1 in 3, not 1 in 5 because the 1 in... refers to the tangent of the angle! Perhaps they should have left well alone. Stan Collins, Marston Moreteyne, UK Re Mr. Spedding's 100 % = a brick wall. If :- 1 in 5 = 20 % 1 in 4 = 25 % 1 in 3 = 33 % 1 in 2 = 50 % angle of 27 deg 1 in 1 = 100 % angle of 45 deg i. e. NOT 90 deg ! Am I doing something wrong ? Martin Dymond, Seaton Devon

theguardian.com - When, and why, did British road signs warning of a steep hill change from ...

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