I would suggest however that in Britain there is a gain to be made in terms of safety because of the mess things are in, qv the problem with “bridge strikes” and other hazards and lack of consistent metric signage for height, width and length.

A complete and decisive change to metric on road signs, coupled with a requirement for vehicles to have an in-cab indication of vehicle dimensions (where appropriate) in metric would eliminate an obvious risk.

The same could not be said of imperial because it would not solve the problem of continental vehicles on British roads or British vehicles travelling to the continent.

The 100 yard markers that John Gow refers to are actually spaced at 100 metres.

When you drive on the Continent (or the UK changes), multiply speed limit in kilometers per hour by 0.5 for a 1.8 s gap, or by 0.6 for a 2.16 s gap. I use this when I drive in Canada.

You could multiply by 5/9 for a perfect 2 s gap, but frankly, there is nothing sacred about 2 s. A little more or less, depending on an individual’s reaction time may be better suited to that individual. Also, most of estimate distance in either yards or meters imperfectly.

At least in the US, a speed limit in kilometers per hour (few are) must be a multiple of 10, so it is easy enough to multiply. I believe Canada also requires a multiple of 10 (or I haven’t driven on Canadian roads with an odd multiple of 5, but even that is easily multiplied by 0.6)

Leaving aside the fact that there would have to be 1800 yards in a mile for his approximation to be exactly correct, can he please explain this “huge advantage”?

As far as I can see, it only works if you are exactly 2 seconds behind the car in front, and travelling at exactly the same speed, and even then, it will only tell you that the distance in yards to the car ahead is approximately equal to your speed.

Personally, all I need to know is that a 2 second gap is the recommended gap to leave to allow me to brake safely. I don’t need to know the exact distance to the car in front.

If I want to estimate 30 metres, I can do it by eye. It’s roughly half the width of a football pitch (touchline to centre spot) That’s hardly difficult to imagine.

It is also a tiresome argument to suggest that imperial units are required for British traffic signs in order to comply with European Union directives. The Units of Measurement directive allows imperial on British signs as a concession (derogation). That is not the same as requiring them.

In any case the TSRGD does not fully comply with that directive, nor for that matter with the UK version, namely the Units of Measurement regulations. The use of ‘m’ for mile (the symbol for metre), ‘T’ for tonne (instead of ‘t’), ‘yds’ for yards (rather than ‘yd’ – unit symbols should not be pluralized) and failure to use ‘ft’ and ‘in’ for feet and inches are all points of departure, none of which are authorized.

Moreover, metric units are allowed by the TSRGD on signs that announce height, width, and length restrictions. It is simply a matter of amending the TSRGD to permit (at the very least) the use of the symbol “m” for “meters” in addition to the word “yards” on signs in the tunnels.

A straightforward design would raise the word “yards” above the baseline of the digits to make room for the symbol “m” beneath it. (Other variations are of course possible.)

The response by Mr. Baker strikes me as fatuous, to say the least. I hope someone on the opposition asks the appropriate question during question time.

In addition to this, the clauses in TSGRD banning metric only seem to have been added in recent years with the badly thought out excuse of “avoiding confusion” and there are plenty of places in TSGRD where metric is permitted (or sometimes even required such as for trams) so it can’t be that difficult to make metric permissible on signs intended for pedestrians!