Amazing that the same sign is used for km/h and mph. - Patrick 10:38 18 Jun 2003 (UTC)

The double sign thing is remarkably dumb, I think it would be a good idea to change it. SimonP 01:28 5 Jul 2003 (UTC)

Fixed dml

<<Traffic engineers are taught the 85th Percentile Rule, which claims that maximum speed limits should be set to the speed at which 85% of vehicles are traveling. (Thus 15% of vehicles are speeding.) The rule has a mathematical basis; the 85th percentile almost exactly corresponds to one standard deviation above the mean of a normal distribution. This rule has been used for many years, yet no scientific evidence has been produced that this particular rule is safer than any other. >>

Is this true? If speed limits were set to the 85th percentile of drivers, then that would mean setting a speed limit would actually raise the average speed at which people take a road, since (at least in the United States) many more than 15% of drivers are speeding at a given time, and most feel compelled to be doing at least the speed limit. In practice (this is just anecdotal observation) the average seems to be 5 to 7 mph over the speed limit, and I'd guess 85th percentile's about +10-15. 137.22.11.145 04:22, 1 Apr 2004 (UTC)

One time a police officer in our area said that he stopped an older man for going 28mph on the interstate when the limit at the time was 55mph. He said that was an accident waiting to happen, that someone going the limit would have come upon him and been unable to slow down or move aside in time.

JesseG 02:34, Nov 20, 2004 (UTC)

Merge with 30 mph

I've done a preliminary merge of the two pages, as indicated in the article. Comment and modify to your heart's desire. Josh 05:22, Apr 13, 2005 (UTC)

Where is Canada's speed limit?

Each province in Canada has its own speed limit laws. Most provinces have a speed limit on freeways of 110km/h except for Ontario and Quebec which have freeways (and toll highways) at 100km/h. Also rural two-lane roads in Canada have a speed limit of 100km/h (as is standard also in Europe and Australia) but in Ontario and Quebec it is only 80km/h. Generally Ontario and Quebec have the lowest speed limits not just in Canada, but in North America. I feel that the Paragraphs in the Article on Canadian Speed Limits is best under the circumstances.

Mph in US and UK only?

Am I right every country in the world uses Kph speed limits except the US and the UK? if so, this article should probably say this interesting fact more clearly. Seabhcán 00:50, 8 Jan 2005 (UTC)

Nobody uses "Kph. They use kilometres per hour whose legal symbol is "km/h". SI units do not have abbreviations, they use symbols that do not vary with language or type.

Hold your horses there, there's another 12 days to go until us Irish finally change our speed limits to km/h (or kph as the signs will say)! zoney ♣ talk 13:35, 8 Jan 2005 (UTC)

The conversion is complete and the signs show km/h not kph. Kph is wrong, wrong, wrong!!!

There may be a few others, but I can't think of them. The US, in fact, doesn't use metric for anything!

Incorrect. 40 % of US industry is metric. Automobile manufacturing is the most visible. With some industries using metric parts and others not, it creates an added cost burden to Americans who have to maintain duplicate inventories of parts to serve both sides.

To make it easier to convert in the real world, the converted speeds here should be listed as follows:

Metric to Imperial: 10 = 5, 20 = 10, 30 = 20, 40 = 25, 50 = 30, 60 = 40, 70 = 45, 80 = 50, 90 = 55, 100 = 65, 110 = 70, 120 = 75, 130 = 80, 140 = 90, 150 = 95.

Imperial to Metric: 5 = 10, 10 = 20, 15 = 25, 20 = 30, 25 = 40, 30 = 50, 35 = 55 (or 60), 40 = 60, 45 = 70, 50 = 80, 55 = 90, 60 = 95 (or 100), 65 = 100, 70 = 110, 75 = 120, 80 = 130, 85 = 140. 24.146.12.62 03:15, 11 Jan 2005

The UK (Where I live) also rarely uses Metric. Milk still comes in pint and two pint bottles, which, due to EU law, are labled as "1.136 l"! Seabhcán 15:13, 11 Jan 2005 (UTC)

I just read in Pint that "The UK pint is officially defined as 0.56826125 litres precisely". So whats the point of using it, if its defined in terms of litres anyway??? Seabhcán 15:16, 11 Jan 2005 (UTC)

UK industry is fully metric as are the majority of prepackaged goods in the shops. Weather is predominately reported in metric, petrol and oil are sold in litres, length products are sold by the metre and most shops use kilogram scales when selling produce to customers, etc. Some milk is sold in litres, others in pints, but the remaining non-metric products compose a remnant not the norm

convenience, and especially tradition. The convenience because there are lots of bottles, etc, made in this size, and also because they are frequently very nicely sized units. Thryduulf 16:36, 11 Jan 2005 (UTC)

Maybe, but when I buy a half litre of milk in Ireland, I don't notice the missing 0.06826125 litres. Personal preference I suppose. ;-) Seabhcán 20:47, 11 Jan 2005 (UTC)

It is what you want to be use to. In Australia milk is sold in 600 mL and 1200 mL sizes. Thus you get 32 mL and 64 mL more. The UK can do the same. BTW, why dis you say "missing 0.06826125 litres", instead of saying "missing 68 mL"? Maybe in imperial that type of nonsense works because imperial doesn't employ user friendly prefixes to scale numbers, but metric does. Maybe you and other luddites might find metric more convenient if you took advantage of its user friendliness instead of trying to incorporate bad imperial practices when using metric. 17:01, 30 Jan 2005 Ametrica

Touché. :-) Seabhcán 20:38, 30 Jan 2005 (UTC)

Proposed reorganisation of article

I think the current layout of the article is a little hap-hazard - without a good logical structure. I propose a reorganisation here: Speed limit/proposed, along with some new sections which need to be writen, such as a proper history section (Speed limits must be a 20th Century invention? Were there limits before the automobile?) and Speed limit enforcement, which must vary greatly from country to country. We're also missing info on many regions of the world, such as Central and South America, Africa, and Russia. What do you think? Seabhcán 01:39, 21 Jan 2005 (UTC)

First thing to do is to throw "kph" out of your vocabulary. Gene Nygaard 01:48, 21 Jan 2005 (UTC)

Why? Its perfectly understandable, and serves as a link to the correct article: Kph. Seabhcán 12:03, 21 Jan 2005 (UTC)

Although I prefer km/h, it doens't really matter to me which is used. However, you should pick one and use it consistently, not mix and match. Thryduulf 12:34, 21 Jan 2005 (UTC)

Wrong. That Kph merely redirects to Kilometre per hour (do slashes work in article names and Wikipedia search engine?), and if you had clicked on that link, you would have learned what the proper symbols are. Even in the United States, our speedometers don't say "kph"—they use the proper "km/h". Gene Nygaard 13:18, 21 Jan 2005 (UTC)

km/h redirects to Kilometre per hour, so yes it does work in the article name and search engine. Thryduulf 13:26, 21 Jan 2005 (UTC)

For what it's worth, km/h is the abbreviation used on our spanking new metric speed limit signs in Ireland. zoney ♣ talk 13:29, 21 Jan 2005 (UTC)

By the way, if you are worried about parallelism, "mi/h" is acceptable, and redirects to Miles per hour (for some reason that one is plural, probably from before preference for singular expressed). Lots of latitude there; English units are like old software, no longer supported and updated--nobody really making any rules for them any more. Gene Nygaard 13:31, 21 Jan 2005 (UTC)

I've made several edits and comments on the /proposed page, along with a couple of typo and spelling fixes. Thryduulf 13:11, 21 Jan 2005 (UTC)

I'm happy with replacing all "kph" with "km/h". Seabhcán 17:04, 21 Jan 2005 (UTC)

"Forces increase exponentially"

Yesterday, I removed the word "exponentially" from the claim that "crash forces increase exponentially as speed increases." Today, Coolcaesar reverted my deletion with the note "Looks like Coneslayer wasn't paying attention in high school physics!" I would like to point out that I hold a B.S. in physics, in addition to a Ph.D. in astrophysics. I will therefore use this space to explain my deletion.

First, understand what is meant by "exponentially." If a force increases exponentially with speed, we're saying: Failed to parse (unknown function \propto): F \propto {\rm e}^v . So let's see if that's the case. The original statement is a bit vague, but let's say it's referring to the average deceleration force, which occurs over a fixed distance d travelled (e.g. the crush zone of the car). We will assume constant deceleration during this interval.

We have then that the car decelerates from an initial velocity v₀ over a distance d at a constant acceleration a. From basic mechanics, x = at² + v₀t (taking x(t = 0) = 0). Now, the end-state occurs when v = 0, also at which time x = d. This is when v₀ = at_final, or t_final = v₀ / a. Substituting, we have , or d = a(v₀ / a)² + v₀(v₀ / a), or finally and hence

Thus, the deceleration (and hence force, since the car's mass is constant) increases with the square of the initial speed. It does not increase exponentially.

You may be able to get different dependences with different assumptions, such as a fixed time, instead of distance, over which the deceleration occurs, but I don't see how to get an exponential dependence, with any reasonable choice of assumptions. If you can, please feel free to illustrate, but don't just point us to the force and acceleration articles, like you did in your edit. -- Coneslayer 22:11, 2005 Mar 24 (UTC)

Oops! Okay, I concede you have analyzed the underlying mathematics quite clearly. I was using exponential (and I believe whomever originally inserted that word also meant the same) in the sense that the relationship is not a simple first-degree or linear function, which is the most intuitive relationship for most people. That is, neither F nor a equals v times some constant.

Of course, having reread several Wikipedia articles on algebra to refresh my own memory, I also concede that exponential is inappropriate since v itself is not the exponent. Perhaps "nonlinear" may be more appropriate. --Coolcaesar 02:00, 25 Mar 2005 (UTC)

US Speed Limits

I will post a US State by State highway speed limit chart. I will also credit the list to the site I found it on, and I hope people occasionally update the chart from time to time.