Height on a road sign: corresponding to metric.

[Pirlouit95]

[P-Henny]

Draw an imaginary straight horizontal line between the two points where the vertical white lines touch the arch.

The sign says that the clearance to this imaginary horizontal line is 13ft 9inches (13' 9"). Thus the height to the very centre of the arch at the highest point is slightly higher.

The justification for this statement above can be found halfway down this web page:

https://www.hgvalliance.com/Helpful-Guides/bridge-strike/low-bridge-finder/uk

13ft 9inches in metric is 4 metres 191mm according to an Internet online calculator I used.

The sign shown is a legacy pre-metrification sign, some still exist on UK roads, this website explains more:

https://metrication.uk/transport/roads/vehicle-restriction-signs/

[Rallymatt]

The photo is distorted so calculating the actual height from that will be difficult.

As a general guide there are basic sets of height signs held in the stores, the indicated height may be accurate but it could also be higher. The metal frame painted white on this one indicates that the height is at least 13’ 9’ within the indicated area

[CORKY.]

Does it really mean 13ft 9inches ?.... NO it doesn't ! This is not a measure of the height, it is a measure of the clearance, which has strict rules for measurement, including..... On a horizontal road, the height is measured accurately, and rounded down to the nearest 3 inches, ANOTHER 3 inches is then deducted. This is the CLEARANCE height displayed on the bridge. On a bridge with an incline approach there are more complicated rules, because an approaching/leaving vehicle roof will be at an increased height, measurements will vary depending on the gradient and it's proximity to the bridge .

[atom3624]

I hope that 13'9" is the minimum height between the pointers, not the maximum - arched bridge and all!

Al.

[Pirlouit95]

Thank you for these responses.

I understand that it is not the height of the bridge at the level of the arch, but the maximum height recommended for a vehicle.

Above, it may catch.

Here is another photo with a vehicle to give an idea of ​​the height.

I actually asked the question because I want to depict a diorama of Berwin Station on the Llangollen Railway and that bridge is the station platform.

And without a landmark, more than 4m seemed like a lot to me.

But with a vehicle underneath, it seems possible.

So I can start my calculations to represent this at 1/76.

Many thanks again for your explanations and the various very interesting links.

[37lover]

CORKY,

You seem to have some knowledge of these matters but are you sure that 3" is added to the measurement [rounding up!] with another 3" added to give the clearance. My simple brain suggests tolerances would be deducted, otherwise there would be quite a few tall vehicles hitting the bridge!

[P-Henny]

Here is another view of the bridge, this time from the other side of it. This view makes the bridge height look far lower than the previous posted views and does not appear to show any resemblance to the previous posted picture with the red car.

[Pirlouit95]

CORKY,

You seem to have some knowledge of these matters but are you sure that 3" is added to the measurement [rounding up!] with another 3" added to give the clearance. My simple brain suggests tolerances would be deducted, otherwise there would be quite a few tall vehicles hitting the bridge!

 

 

Here is what it says on https://metrication.uk/transport/roads/vehicle-restriction-signs/

IMPERIAL HEIGHT

To obtain the imperial figure shown on the signs, the deck height is measured in feet and inches, rounded to the nearest inch.

3 inches are subtracted from the measured value.

The remaining value is then rounded to the nearest multiple of 3 inches.

The bridge is signed with the rounded value in feet and inches.

 

 

If I understand correctly:

The measurement of the bridge equals 14' 7"5/8.

Round up to the nearest inch, which is 14' 7".

3 inches are subtracted from the measured value, resulting in 14' 4".

The remaining value is then rounded to the nearest multiple of 3 inches, resulting in 14' 3".

Is this correct?

 

 

 

 

[37lover]

Pirlouit95,

Not quite. If you round up to the nearest inch then 14' 7"5/8 becomes 14' 8". I am surprised that it is not rounded down to the nearest inch, which would then be 14' 7" and your example would be correct.

14' 8" minus 3" becomes 14' 5" and rounding to the nearest multiple of 3" results in 14' 6".

Way too much thought for a picture/model of a simple bridge.

[What About The Bee]

Delta solution 1 v 2

14'6" - 14'3" = 3"

OO Scaling

3" / 76.2 = .03937"

Convert to metric

.03937 × 25.4 = 1 mm

The difference between solution 1 and 2, in OO, is 1 mm.

The height is measured from the crown of the road in the US. Perlouit95 must therefore also control the surface of the road, including its crown, relative to the underside of the bridge, including its arch.

To 1 mm.

~~~~

Hi Perlouit 👋

Unless you are 3D printing the bridge and the road as one unit, it will be difficult to control all of the dimensions precisely. If your bridge is slightly off compared to the real world, the only one to notice will be you! When you consider the OO squish (for the non scale track) a minor height error becomes insignificant.

I understand striving for perfection. But I also understand providing tolerance for components. If this were me, I would easily accept plus or minus 1 mm for the bridge clearance.

Bee

[atom3624]

This happened in Glasgow today!!

HOW?

[Going Spare]

Many mitigating circumstances; not necessarily just carelessness on the driver's part.

The signage is not totally accurate as a 2.5m wide vehicle should not be able to pass through a 2.2m gap. If the physical width restriction was as per signage, the bus could not reach the bridge, which suggests the bus was off-route for some reason.

[atom3624]

Certainly, but there's no 'arch', it's a perfectly perpendicular crossing / bridge, wide enough, and surely on an established route? The road surface shows little variation either, so 2.5m or 5m wide wouldn't make much difference, and certainly not to effect such a catastrophic dimensional discrepancy - removal of half the upper deck!

Whatever training, route selection, etc., may have existed previously, surely 'in modern times' one would have thought this should be covered in modern day ... but it did happen!

I'm sure that 'went down well'!!

Al.

[What About The Bee]

There is a bridge which is quite famous for being struck.

11'8" posted clearance. There are automatic sensors, with stop lights, informational signs & etc. It has everything needed to prevent a strike.

It was struck so many times, the railway raised the bridge by 8" to 12' 4", at enormous cost. Didn't work. Still being struck.

The proof?

178 videos, most of which are the bridge being struck. Not the aftermath, the actual strike. There are a handful of videos wherein there is discussion.

https://youtube.com/@11foot8plus8

Bee

[Moccasin]

Quite surprised they received funding and approval to rebuild the bridge to a height which still left it substantially below standard highway clearance.

Minimum clearance in highway standards is 16’6” (5.03m). A lot of money to spend when not actually removing the risk and when substantial mitigation is already in place. Sacrificial beams either side of the structure would have probably been a better investment!

[What About The Bee]

Hi Moccasin

Structural beams are in place.

Bee

[96RAF]

This happened in Glasgow today!!

HOW?

 

 

Viewed from the other side you would see two bridges the second being lower than the first.

[atom3624]

The only point I meant really was that if it's on 'a major bus route' this should be automatically verified, surely .... !!

Perhaps there were some of the 'last minute before end of financial year' local council roadworks and an enforced diversion ... or a bus type change through necessity / availability.

Al.

[Moccasin]

Yes bus routes will be checked beforehand. These incidents usually happen if a road closure or other issue diverts buses off their normal route, or (rarely) if a double deck bus is mistakenly assigned to a single deck route due to disruption etc. still doesn’t absolve drivers of blame as there are always warning signs and double deck buses have broadly consistent heights, though shorter double deck buses are available (used in Oxford for example).

Go North East double decker buses around here also have audible alarms fitted to their vehicles which warn drivers of “low bridge ahead….. 100 meters”

A bit disconcerting for passengers as they warn of all low bridges in vicinity, rather than those actually on the route!

[Pirlouit95]

Hello everyone.

Thank you very much for all your very interesting answers.

Strange this bus accident. Even if it is not the planned route, the driver must know the height of his vehicle and know if it passes or not. Especially since it's not a few small centimeters removed. Or maybe it's his first time driving a double-decker and he's forgotten.

To return to the original subject, I asked this question because I am in France and I do not know the British measurement system. And in the first photo, without a landmark, it looked small compared to the dimension on the panel. But in the photo with the SAAB it looks correct.

I discovered the British railways by watching television series (Hercule Poirot, Miss Marple, Barnaby, etc) which we adore Madame and me. And I fell in love with these railways. I had already talked about it on this forum, a long time ago, but I was very ill and I remained absent all this time. Now that I'm better, I'm going to start model railroading again.

I want to make a small UK-inspired network and while researching I came across the Llangollen Railway and its Berwyn station. Of course, I will not represent it 100%, but simply an evocation. Just as I do not wish to represent a particular company.

Well, sorry for the novel. I will come back to you for other questions later and on another thread. Many thanks again for all your answers.

[96RAF]

Good to hear that you are well again and can enjoy the hobby.

Here are some more images of low bridge markings and associated signs and warning methods https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjHza2tpon_AhVTHsAKHSLpAh8QFnoECCEQAQ&url=https%3A%2F%2Fwww.istockphoto.com%2Fphotos%2Flow-bridge-sign&usg=AOvVaw1x1J31_F_0EsH-vDprAalD

[Moccasin]

Welcome back to the hobby and while we may have gone somewhat off-topic in answering your question, I hope that the background information has been useful & inspiring.

[P-Henny]

To the mods.

I believe "correspondence in metric" in the thread title should read more like "corresponding to metric". Since it is questioning the corresponding metric equivalence to an imperial measurement and nothing to do with writing letters etc.

If you do edit the title, then feel free to delete this post.

[Pirlouit95]

Thank you PH for this information. I use Google translation and the grammar is not always respected. And in French, the two expressions mean the same thing. I made the correction, but I want to leave your message. Feel free to correct my mistakes, it's learning.

Thanks again.