HS2 Speed Units (MPH or km/h)

[edwin_m]

Weren't we talking about whether or not HS2 would be in MPH or km/h?

I think that was confirmed at about post 3. Why let a good thread go to waste?

 

[Mcq]

Standard Gauge - that's British and here to stay

 

[notadriver]

I dislike digital speedometers - you can’t really tell your rate of acceleration or deceleration. I prefer to have both analogue and digital. The ERTMS unit inside trains fitted with it has both but TVM430 uses purely digital readout although the up and down arrows help. Maybe it’s because with a digital speedo you are more aware you aren’t doing exactly the speed limit ?

 

[Ianno87]

Standard Gauge - that's British and here to stay

And defined in Millimetres.

 

[Mcq]

And defined in Millimetres.

Is nothing sacred!

 

[Ianno87]

Is nothing sacred!

I believe you'll need to go back to the 1960s for when it was last defined in imperial measurements....

 

[Mcq]

I believe you'll need to go back to the 1960s for when it was last defined in imperial measurements....

Well at least we still measure distances in miles and chains - don't we?

 

[Ianno87]

Well at least we still measure distances in miles and chains - don't we?

On most infrastructure, yes. Notable exceptions being HS1, the Cambrian Route (due to ETCS), light rail systems, plus Electrification masts since the 1970s.

New infrastructure (e.g. signalling design) is always done in metric.

 

[JN114]

On most infrastructure, yes. Notable exceptions being HS1, the Cambrian Route (due to ETCS), light rail systems, plus Electrification masts since the 1970s.

Heathrow Branch is also entirely metric for distances from the infrastructure boundary at the tunnel portal, with regular meterage markers along the tunnel walls. Line speed still shown in mph for now, although trains on ETCS L2 are running on km/h

 

[Mcq]

Thanks for the detail - in part I was attempting a bit of humour to a British standard. I find we're best at that

 

[edwin_m]

Standard Gauge - that's British and here to stay

We must like gauges - several of the others that are still common also originated in the UK or what was then the British Empire.

 

[DelW]

Well at least we still measure distances in miles and chains - don't we?

New road alignments have been designed in metres and derivatives at least as far back as the early 1970s, when I joined the industry.
But distances along the centreline were (and probably still are) referred to as the "chainage", although they were in metres.

 

[AM9]

Standard Gauge - that's British and here to stay

Yup, it's 1.435m and recognised in most countries.

 

[MichaelDono]

I've heard the Thameslink Core is signalled in kph when under ETCS, is that correct?

 

[edwin_m]

New road alignments have been designed in metres and derivatives at least as far back as the early 1970s, when I joined the industry.
But distances along the centreline were (and probably still are) referred to as the "chainage", although they were in metres.

So are rail projects.

Miles and chains for distance, and mph for speed, are still there because of the upheaval and possible safety hazards in changing all the operating paperwork and signage, and re-training the workforce. Introduction of ERTMS on a particular route would involve a similar amount of operational disruption even if the old measurements were kept, and incidentally fits all the traction using that route with speedometers that work in km/h. So best to change it route by route as they go over to ERTMS.

 

[plugwash]

You have to use radians to measure angles - calculus doesn't work at all if you don't.

Nothing stops you from writing out the set of differentiation and integration rules for the degrees or gradians version of the trig functions. They just won't be as neat as the rules for the radians versions of those functions.

 

[Maurice3000]

The continuation of air traffic altitude measurements in feet is a by-product of US domination in aviation.
Ironically, the Nautical Mile is more in the concept of metric linear measurement in that it is derived from a physical dimension of the earth. In reality, it has no connection with a statute mile other than by part of it's given name.

Fun fact, the use of feet for altitude in aviation is not a global thing. Countries that developed aviation outside of American influence use metres for altitude and flight level. Mainly Russia, China and surrounding countries and countries that used to be part of the Soviet Union or in its sphere of influence such as large parts of Central Asia.

If you fly from feet airspace to metre airspace there is a transition zone to adjust to new flight levels and pilots always fly with conversion charts. Modern planes can also switch some of their instruments from one system to the other.

There is also the fun thing of runway length being in metres everywhere except the US, though visibility distances are apparently in metres in the US too. The International Civil Aviation Organization has recommended that the entire sector switches to metric to sort out the mess but I don't see that happening quickly.

 

[BayPaul]

Other than literally being invented by the Brits when Empire building...

Arguably it's the most Imperial unit there is. And the first target of the metric system, which hated the sexagesimal angular measurements.

Metric started by replacing the nautical mile with the kilometre (well, OK, it started with the centimetre), which is a centigrad of arc (not that there was a gradian at that point) - instead of a sixtieth of a nintieth of a quarter of the earth's circumference, metric's initial move was to replace it with a hundredth of a hundredth of a quarter. Before the pound or the minute (and they did try there) or the gallon, the metric system came up with a replacement for the nautical mile.

Sure, the abject failure of gradians to replace degrees meant that metric started tolerating the nautical mile after about 120 years (about 110 years ago), but it isn't part of the metric system and was deliberately targeted by the metric system for replacement right from the get go.

The nautical mile is a very practical form of measure on ships - as it is direcly comparible to latitude (one minute of latitude = 1 NM), so it would never have been possible to use KM (without resizing the earth to match). So many calculations, measurements on charts and so forth rely fundamentally on this direct link, it would never be practical to use a unit that isn't an exact fraction of the circumference of the earth.

 

[si404]

The nautical mile is a very practical form of measure on ships - as it is direcly comparible to latitude (one minute of latitude = 1 NM), so it would never have been possible to use KM (without resizing the earth to match).

Why is a minute of latitude any different for ships to a centigrad of latitude? Other than we don't use gradians, of course...

There's no need to resize the earth to use km (though both units aren't quite right as the earth isn't perfectly spherical). The 'problem' is that metric angle measurement failed to take off and we continued to use degrees.

The nautical mile is an imperial unit that metric tried and failed to replace.

 

[BayPaul]

Why is a minute of latitude any different for ships to a centigrad of latitude? Other than we don't use gradians, of course...

There's no need to resize the earth to use km (though both units aren't quite right as the earth isn't perfectly spherical). The 'problem' is that metric angle measurement failed to take off and we continued to use degrees.

The nautical mile is an imperial unit that metric tried and failed to replace.

Oh, that would have worked. But i don't think a KM is exactly a gradion of anything (I'm happy to be corrected if I'm wrong). The nautical mile is defined based on latitude, so the oblate spheroidness of the earth doesn't matter too much for the calculations.

 

[si404]

But i don't think a KM is exactly a gradion of anything (I'm happy to be corrected if I'm wrong).

The centimetre was initially defined as a billionth of the distance from the North Pole to Equator through Paris (then the length of a stick, then this distance light travels in a specific time). A kilometre is therefore 1/10,000 of the the quarter circumference, or a hundredth of a hundredth. It's a hundredth of a gradian of latitude, or a 'centigrad'.

The nautical mile is defined based on latitude, so the oblate spheroidness of the earth doesn't matter too much for the calculations.

A minute of latitude is about 1861m at the poles and and 1843m at the equator, with the international nautical mile 1852m (rounded from 1851.85m obtained by definitions - 90*60NM = 100*100km). The real number for the distance between north pole and equator is 9985km, rather than 10,000km. But, yes, the slight differences are pretty much irrelevant.