That never happens to motorists because the roads are rarely designed by people who don't drive. For cycling, that's not often false than true, unless you consider people who know how to ride a bike because they did it as a child as falling into the "true" bin, or people who never ride outside some vacation resort, and never faster than 10 mph.

Cycling infrastructure designed by people who don't cycle is far too common.

A favourite example I have to deal with often is when the path has to narrow, so they put up signs telling all cyclists to dismount. I pass through a few of these often, and whenever a cyclist obeys the sign it creates immediate congestion because pushing a bike is slow and takes up more space. Then you get a cascade effect of pedestrians stepping into car traffic to avoid the bottleneck.

Another is rumble strips to slow down bikes at pedestrian crossings. It doesn't slow anyone enough to prevent incident, and tends to give pedestrians an illusion of priority so they stop looking for bikes in the path. Not to mention being uncomfortable enough to discourage using the bike path at all, and shaking lights out of position.

> Another is rumble strips to slow down bikes at pedestrian crossings.

Do you by chance mean those things on the ground with the raised dots/grooves? [1]

Those are actually for helping the blind navigate it. If it is something different JUST to slow bikes though... That just makes me go WTF.

[1] https://cdn.w600.comps.canstockphoto.com/man-walking-on-yell...

Probably no.

But there is a guideline that you should only go at the speed from which you can stop from within the visible part of the road.

And yet roads are full of highly visible warning signs whereverr there is a turn that might not be safe at slightly beyond general maximum speed in some weather conditions.

I'm not sure I've seen weather condition specific warning signs, apart from the speed limits being lowered for the winter season by swapping the signs themselves.

Can you link to an example?

They're pretty common in some places. The E17/A22 entering France for example has these overhead signs[0] that go from 110 in good conditions down to 70 in very bad conditions or even 50 if there's congestion. There are also similar signs in Belgium but they're more rarely adjusted depending on weather, it's usually just according to traffic.

[0] https://maps.app.goo.gl/pbCArbN5yraJZFBw9

I can’t seem to find a link, but I know there is a fog-prone Interstate zone in eastern Tennessee (probably I-81, might be I-40) with variable speed limit signs not terribly different from those on UK smart motorways.

Hungary has an elegant, low-tech solution. Broad white stripes are painted ~100 m apart on the shoulder of the road. Fixed signs indicate the allowed speed - if you can see three, it’s 130, two is 110, one is 80 (or something like that - it’s been a few years).

I wasn't even referring to signs that are only applicable in specific weather conditions, just pointing out the absurd amount of handholding drivers tend to get. Some drunk chump might run straight into the trees? Add more reflective chevrons. Someone still crashed? Add flashing LEDs.

And yes, German signage certainly does weather dependency, speed limits with "Zusatzzeichen 1052-36" are quite frequent (I think it's put up everywhere the surface doesn't drain as good as it should, e.g. if surface angle changes slightly from the ground setting after construction)

The UK's "smart motorways" project does this. https://en.wikipedia.org/wiki/Smart_motorway

Actually turns out they're a terrible idea, tbh.

> Would it be in anyway acceptable for someone to plonk an unmarked concrete block in the middle of an unlit road?

You mean like the "traffic calming measures" most urban roads have, to slow down cars?

Traffic calming measures, unless implemented entirely incorrectly, are not unmarked. To have them unmarked would defeat the purpose, which is to indicate that the driver of the vehicle attempting to navigate the street must slow down. It is not in the interest of those living on a street with traffic calming measures to have drivers cross the traffic calming measure at a high speed.

Narrow or winding roads, or roads with no central marker are calming techniques often unaccompanied by signage

Okay, but many of those traffic calming measures are a big concrete block in the middle of the road.