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 Post subject: Speed Limit
PostPosted: Sat Oct 29, 2011 09:38 
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Greeting everybody

we have a straight 1.8 Km street ( from one traffic signal to another) with 4 lanes ( each lane approx. 2.7 m) and one shoulder.

How to calculate the speed limit for cars in this street?
Kindly provide me with simple rule for calculating that, with reference.

note: with ignoring weather condition.

Regards


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 Post subject: Re: Speed Limit
PostPosted: Sat Oct 29, 2011 12:02 
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In MPH it would be...

(2Pi * (Radius of any camber)) / Cos(slope of the road in radians) * Mean vehicle weight * (Coefficient of friction of the surface) / (average daylight hours) / magnetic inclination * 0 + 60

But that is assuming the UK, so if you could advise us of the territory, any buildings near the carriageway, the existence of street-lights, higher risk communities such a schools and hospitals nearby, etc. we could probably fine-tune things.

;)

mb


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 Post subject: Re: Speed Limit
PostPosted: Sat Oct 29, 2011 16:39 
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nostalgia wrote:
Greeting everybody

we have a straight 1.8 Km street ( from one traffic signal to another) with 4 lanes ( each lane approx. 2.7 m) and one shoulder.

How to calculate the speed limit for cars in this street?
Kindly provide me with simple rule for calculating that, with reference.

note: with ignoring weather condition.

Regards

Are you referring to roads in the UK? (your registration email address suggests otherwise).

A quick Google.

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 Post subject: Re: Speed Limit
PostPosted: Sat Oct 29, 2011 17:12 
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To be honest, in the UK speed limits are generally determined from the nature and level of development on the road, and the casualty rate, not the road geometry as such.

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 Post subject: Re: Speed Limit
PostPosted: Sat Oct 29, 2011 20:55 
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PeterE wrote:
To be honest, in the UK speed limits are generally determined from the nature and level of development on the road, and the casualty rate, not the road geometry as such.



Hmnn, In my experience of Local Government, Speed limits are largely determined by retired/semi-retired people who are of the opinion that somehow the world would be Soooo much a nicer place if people drove rather more slowly!

(No Im not kidding, In all seriousness the level of debate was no more than "Wouldnt it be nice to have a :40: along "Windermere avenue" instead of the current :nsl: " :x :roll:

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 Post subject: Re: Speed Limit
PostPosted: Sat Oct 29, 2011 22:37 
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boomer wrote:
In MPH it would be...

(2Pi * (Radius of any camber)) / Cos(slope of the road in radians) * Mean vehicle weight * (Coefficient of friction of the surface) / (average daylight hours) / magnetic inclination * 0 + 60

But that is assuming the UK, so if you could advise us of the territory, any buildings near the carriageway, the existence of street-lights, higher risk communities such a schools and hospitals nearby, etc. we could probably fine-tune things.

;)

mb


Cough!, er, I think you'll find that ought to be the Sin of the slope of the road... :wink:


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 Post subject: Re: Speed Limit
PostPosted: Sun Oct 30, 2011 18:06 
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Mole wrote:
Cough!, er, I think you'll find that ought to be the Sin of the slope of the road... :wink:


And I think he means magnetic declination :loco:

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 Post subject: Re: Speed Limit
PostPosted: Sun Oct 30, 2011 20:30 
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Thank you gentlemen for your reply.
Quote:
Are you referring to roads in the UK? (your registration email address suggests otherwise).


I am not in UK.


boomer wrote:
In MPH it would be...

(2Pi * (Radius of any camber)) / Cos(slope of the road in radians) * Mean vehicle weight * (Coefficient of friction of the surface) / (average daylight hours) / magnetic inclination * 0 + 60
mb


:headbash:
This very difficult formula I don't have all these parameter.
is there any other formula simpler than this?


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 Post subject: Re: Speed Limit
PostPosted: Mon Oct 31, 2011 10:28 
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Apologies, Nostaligai - and :welcome:

I think there's a little joke going on! There is no "formula" (that I am aware of) for "calculating" a speed limit. Here in the UK, speed limits were originall set using the "85%ile rule". It just meant that they surveyed all the free-moving traffic and set the speed limit on that road as the speed that 85% of vehicles did not exceed. That was many years ago though - and now we have several speed limits depending on what sort of road (in town, motorway, country roads etc). Increasingly, they are just "randomly" revised on a local basis, but I don't think there's any real "science" behind the selected speeds - only the assumption that "slower-is-safer". :roll:


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 Post subject: Re: Speed Limit
PostPosted: Mon Oct 31, 2011 17:12 
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I think the present "safety" formula for speed limits is something like. Take the present speed limit, subtract the 85percentile speed, add the number of houses in a given mile (up to a maximum of two) and then divide by the number of councillors and old ladies that live within a twenty mile radius of the road in question.

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My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.


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 Post subject: Re: Speed Limit
PostPosted: Tue Nov 01, 2011 11:49 
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Nearly correct there, Graball, but you forgot to mention subtracting the final figure by the amount of cats the old ladies own and factoring in whether Countdown has been memorable that day or not quite up to scratch. Both important considerations.


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 Post subject: Re: Speed Limit
PostPosted: Tue Nov 01, 2011 12:16 
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Tsk tsk, I don't believe y'all missed the most important bits .... I am of course referring to the casting of the chicken bones, and the turkey's bottom kissing ceremony, without which speed limits cannot legally be set :lol: :roll:

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 Post subject: Re: Speed Limit
PostPosted: Tue Nov 01, 2011 13:59 
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I thought it was now based on what Brake suggests and the DfT then double it. So all :30: limits will become :20: because Brake believe we should all be doing 10 mph maximum on those roads. All :nsl: S/C roads should be :40: because they advocate :20: and so on...

Image

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You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.


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 Post subject: Re: Speed Limit
PostPosted: Wed Nov 02, 2011 14:44 
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I appreciate your input Tone, but how can the DfT take Brake seriously without, as brother Zippo mentions, the casting of the chicken bones and the kissing of the turkey's bottom? The end result may appear as if the DfT has just merely doubled Brake's suggestions, but speed limits would lack basic scientific foundations if the chicken bones and turkey bum rituals were not observed. I shudder to think what that world would be like then. People would largely ignore them and set their own speed limits, I expect. Madness.


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 Post subject: Re: Speed Limit
PostPosted: Wed Nov 02, 2011 17:36 
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DoktorMandrake wrote:
People would largely ignore them and set their own speed limits, I expect. Madness.

Nah nah nah ..... wot yer do ya see is, tell everyone its nearly always speed wot done it, then spend half the gdp of the country on speed enforcement dodas which all the drones are gonna support cos they actually believe wot thems is told. That'll make everybody obey the speed limits right? And if they don't, fine em senseless and make a huge big pile o cash.

Now yer got alls those lurvelly fines comin in, yer can take that huge big pile o cash straight over to Greece an flush the lot straight down the nearest toilet instead of spendin it on rubbish like findin out wot actually might cause a lot o RTA's, an doin summat about it. :cry:

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 Post subject: Re: Speed Limit
PostPosted: Thu Nov 03, 2011 03:17 
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Good plan. I like your thinking. Ever thought of standing for parliament? I think you'd fit right in :lol:


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 Post subject: Re: Speed Limit
PostPosted: Wed Dec 21, 2011 21:44 
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:welcome: nostalgia
nostalgia wrote:
...is there any other formula simpler than this?
Might I ask what you are trying to solve?

As Mole states the speed limit setting in the UK has been around the 85th%ile and in more recent years the 'average mean' speed of traffic has been used, although many local Councils do not come to their own conclusions and science is sadly less used.
We campaign for a return to the 85th% setting of speed limits as this provides the safest roads in the UK. The US has also used this system too for years.

Typically as people tend to slow when danger or potential danger is more likely therefor watching what people do is very helpful. Speed limits for most urban environments are set to 30mph ad more open rural roads set to a 'National Speed Limit' of 60mph.

(I feel that I ought to apologise that a few posters have gone off tangent, and not provided winks or other smilies, to indicate their less than sincere answers.)

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 Post subject: Re: Speed Limit
PostPosted: Thu Dec 22, 2011 09:53 
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:welcome: nostalgia

If it helps, think of the 85th percentile as something you do in everyday life, like getting dressed.

We wear appropriate raiment for the conditions so, for instance, on a day like today I am wearing my motorcycle jacket and jeans to get to work and when I get in the building I take them off and put my smart trousers on, a shirt and replace my protective Sidi boots for proper shoes.

When I look around I see that everyone else is wearing similar. We are not overdressed because it would be uncomfortable and too warm but we’re not going around in our underwear either.

Current policy, in relation to what the speed limits are being set at, are like someone telling me I should either be naked or in a flying jacket and bear little relationship to the prevailing conditions or appropriateness. :D

How many out of ten for my analogy? :lol:

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.


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 Post subject: Re: Speed Limit
PostPosted: Thu Dec 22, 2011 17:13 
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Re: Speed Limit

New postby Big Tone on Thu Dec 22, 2011 8:53 am
:welcome: nostalgia

If it helps, think of the 85th percentile as something you do in everyday life, like getting dressed.

We wear appropriate raiment for the conditions so, for instance, on a day like today I am wearing my motorcycle jacket and jeans to get to work and when I get in the building I take them off and put my smart trousers on, a shirt and replace my protective Sidi boots for proper shoes.

When I look around I see that everyone else is wearing similar. We are not overdressed because it would be uncomfortable and too warm but we’re not going around in our underwear either.

Current policy, in relation to what the speed limits are being set at, are like someone telling me I should either be naked or in a flying jacket and bear little relationship to the prevailing conditions or appropriateness. :D

How many out of ten for my analogy? :lol:


Brilliant analogy, Tone.
Sorry though, you will never get a job in road safety or highways planning, you are far too sensible and intelligent.

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My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.


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 Post subject: Re: Speed Limit
PostPosted: Thu Dec 22, 2011 18:07 
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DoktorMandrake wrote:
I appreciate your input Tone, but how can the DfT take Brake seriously without, as brother Zippo mentions, the casting of the chicken bones and the kissing of the turkey's bottom? The end result may appear as if the DfT has just merely doubled Brake's suggestions, but speed limits would lack basic scientific foundations if the chicken bones and turkey bum rituals were not observed. I shudder to think what that world would be like then. People would largely ignore them and set their own speed limits, I expect. Madness.



on't see any mention if the County Council officer .S o a road set at 50 in one county dould be 30 in another .I jest not ,and the opinions of the experts -what's left of Trafpol - just plain ignored , well in Warks anyway .

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