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Comment by herghost | Hacker News Reader

This gives me a newfound respect for variable speed signs on UK motorways (NB. not the actual speed limit signs, the black signs with the white matrix of bulbs giving advisory speeds).

To-date, if you see a sign saying "40", that basically means there's no traffic flow and you will have to come to a stop very shortly.

If you see a sign saying "60" that means that you probably won't need to stop but you're going to slow to a crawl.

If everyone just did as it said things would probably improve massively.

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"40 - Queue ahead" by a junction about an hour after the traffic has cleared. A couple of weekends ago I drove past 3 lane closure warnings and low speed limit signs on a motorway with, you guessed it, no lanes closed.

To some extent this is my confirmation bias, but certainly as often as not the signage is spurious and that's why people don't pay any attention to them. I suspect most people agree with the principal of the things, but every time they obey a sign whilst everyone else flies past, only to discover it was inaccurate it does affect the amount of credence future signs are given.

Lowering your speed will technically resolve the congestion, but your average speed will still be the same as if you had simply "ridden the wave," that is, proceeded at normal speed up to the jam, then proceeded thru the jam at slow speed.

Essentially you are doing a "smoothing" operation if you proactively reduced your speed ahead of a jam.

Hmm, stop-and-go is less efficient though. I try to average things out myself to maximize fuel-economy in those traffic conditions.

Even with regenerative brakes, the regeneration isn't fully efficient. You lose energy to heat. So smoothly traveling one speed is superior.

And human psychology is an important factor here as well. Less stop-&-go means fewer temper flares & physical opportunities for collision.

This gives me a newfound respect for variable speed signs on UK motorways

I respect the idea, but the actual implementation feels a bit half hearted to me. They need to kick in a lot quicker and be more severe, all they seem to do is make a minor improvement and slow people down perhaps a half mile from the actual congestion.

We have variable speed signs in the US, but where I live, they aren't followed, to the point that it seems unsafe to obey them and go 30mph when the flow of traffic is 60mph

Those variable speed limit signs are meant to be enforced by average speed checks with cameras. I'm not sure what's going on with that, I know there are delays, but there's signage that says there are regular speed cameras.

So if the cameras work, we'll have to do exactly what they say or get fined for speeding.

On the new 'Smart Motorways' there is built in enforcement via cameras. On those, the speed limit signs are actually speed limits, with the red ring around them.

The ones I was referring to are advisory and look like this [0].

[0] https://www.drivingtesttips.biz/images/motorway-advisory-spe...

I got hit by this a while ago. Was driving down an empty freeway at night and there must have been road works off the side of the road during the day but I didn't see it until the second sign but the speed camera was after the first sign and I got hit with an $800 fine :/

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