Sounds logical on a just consider it level.

But us old farts know better.

The nation went metric in 1965 joined the EU in 1975.

You know how all road signs are reflective. Well, back then that did not exist. Reflective roadsigns started in the early 1980s.

Add to that, most major roads end up replacing the signs every several years.

And the simple fact is No If in the 80s we decided to double sign (as other nations did. Every nation in the EU did it at some point. France was well before road signs, 1795 I think. But the rest of the EU could not agree on anything before the 1940s. Almost all of them had their own versions of imperial like units divided over regions based on political power.

It was not until the early predecessor to the EU post ww2 that most of Europe changed.

If we started in 1980 by displaying km plus mph on all signs. (Rounded to the nearest unit). The original change would not have cost any more than current spending. Buy now, most major roads would have had many replacements, likely dropping the mph.

We would still see some dual signs in very low use back roads.

But when did you last see a non-reflective sign. Because that is as often as you would see MPH only signs. At 0 extra spending.