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Comment by bombcar | Hacker News Reader

I am actually slightly surprised that road signs haven't been updated to include something like a "barcode" or similar that would make it very easy for the machine to identify what sign it is. You could "paint" over the entire sign with a variation in the infra-red reflectivity with a QR code, for example.

Then the computer would be better at recognizing a sign than a human.

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Back in the late 2000’s I wanted to start a company that broadcasted the current speed limit near signs. Like a BT beacon, sorta, but obvs not BT. It turns out this requires too much coordination. Specifying a protocol, getting manufacturers to build it in, lawmakers to pay for it, sign makers to embed it, etc.

The tech is the easy part.

Isn't this solved by GPS and maps with speed limit data? Google maps gives me nonsense speed limits in a couple of places but mostly correct.

No, because the lower speed limits posted on flashing signs for construction are an important local case.

In my experience, Google just thinks those are traffic jams. I've seen Maps 'know' about road construction speed limits, but it isn't usual.

Good point. Also, M25 (London orbital motorway) has large sections with variable speed limit. Google maps navigation just doesn't show a limit for those areas, since it does not have timely data.

Also the 20mph boroughs really confuse the systems (cars and satnav), since they very often say 30 in 20 and also 20 in a 30. The various limits are, admittedly, not well signed, and I suspect that's deliberate to keep drivers cautious.

One problem is "map matching". That is, given your lat/lng (or, more realistically, a time-series of lat/lngs) and a map, figure out which road you're on.

The thing is that most consumer devices with GPS (like phones and even standalone GPS navigators) have a lot of internal "magic" to hide the raw noise in location fixes from the GPS signal.

For example, certain Garmin devices (intended to be used off road) will snap your location to an Interstate if you are going more than 55 mph and heading roughly in the direction of the road (which is evident when you run into traffic and your location keeps switching between the frontage road and expressway--the error distribution of the noise doesn't have mean=0!).

Out of curiosity, how did the tech deal with things like frontage roads that have much lower speed limits than the highway right next to them.

Basically, they haven't, or at least they hadn't 4 years ago when the car I have with it was made.

Diving along a free flowing 50 and having it decide it's now a 30 because it saw a sideroad and drop a gear is semi-regular. The second most dangerous thing it does after having a touchscreen.

It also manages to read 45 sometimes but I have literally never seen a 45 sign.

Radio waves can be directional. So they were pointed at the road they influenced, not the highway.

If embedded in the sign, what if the sign itself is rotated or damaged in some way?

Our prototype just screwed onto the sign post and could be aimed that way. We never added it to the prototype, but having an accelerometer added to detect movement and shutting down/calling home would help with damage or vandalism.

This would probably be easy to exploit. Someone could drop a bunch of random invisible stop signs.

to be fair someone could also go toss a steel bar on some railroad tracks or drop rocks from the top of a highway overpass.

Right, but that's rather obvious.

It's true that people aren't often looking for fatal pranks, but you could do more benign like try to get people pulled over by causing them to speed unknowingly.

Someone could really just weld a steel bar onto a railroad track out in the wilderness and derail a train??

Are you genuinely asking about the feasibility? If so, then: yes.

Yes. Railroad tracks in the middle of nowhere are usually freely accessible. Why bother putting a fence if no one's around? Even at railroad crossings in cities, one could cause a some collateral damage by welding it right next to the crossing.

Yes? No welding required, just a few thumbscrews, if you use one of these:

https://westernsafety.com/nolan-portable-derail-pd-2/

On sale now! Or pick this one for bigger and faster trains:

https://www.aldonco.com/store/c/127-SaberTooth-Portable-Dera...

There are lots of tools, weapons, chemicals, and other things that a person could do that would be bad. It doesn't take much creativity, just a callous disregard for other people. But in contrast to the fearmongering and crime you'll see in the media, consider it a bit of good news that in spite of how incredibly easy it is to intentionally cause harm to someone else, billions and billions of people choose not to do that every single hour of every single day.

I mean, you now have told a lot of people that you can just get a tool to derail a train easily, that I'd guess most (I didn't) don't even know it exists.

I think that's GP's point: derailing a train is just a search engine away, and that's only scary when we think about it, which we almost never do.

Which in turn is because our emotions around people setting out to do that, are calibrated around the fact that it basically doesn't happen outside of war conditions.

I googled how to do it just for lulz and got youtube video with someone showing one... and some russian/ukrainian looking name in comments asking about it and asking where to get one, from like a month ago

https://www.kyivpost.com/russias-war/anti-putin-russian-rebe...

I wonder whether it's related. Probably not but train derailments are weirdly relevant to current world state...

But back to the topic... I don't think anything should be censored and am of opinion freedom of speech just need to be taken wholecloth, good with the bad, but you gotta wonder how much easier it is now.

You don’t even need to weld it, you just need to leave it somewhere in the way and striking it at sufficient speed will result it in bludgeoning through a car or worse.

An improperly stored rail from a maintenance project derailed a NYC subway train in 2017: https://apnews.com/article/a6a01e5928f9478bab0d33f03260870e

Its hard to derail a train.

https://youtube.com/watch?v=agznZBiK_Bs

AFAIK, at least in Russia there are signaling systems that will interpret a metal object connecting the rails as "another train is on the track" and inform the train driver.

Not sure whether those systems are also installed in the wilderness though. But it seems kinda likely that anybody thinking "I should derail a train for fun" might not bother driving into the wilderness when there's an alluring, convenient, seemingly unobserved stretch of the railway available nearby.

Edit: another thing that comes to mind is that you'd also have to find a low-visibility part of the railway, even in the wilderness — because otherwise the driver will just notice the obstacle and stop the train.

Tag the coded signs on a GPS map. If the detected "sign" is not on the GPS map the system can label it as "probably malicious".

Plenty of places have no reliable GPS reception.

Then why use the signs at all rather than just use this gps based road rule database

Because not all cars are self-driving or have the ability to access this hypothetical database. That will remain the case for likely the next 30 or more years.

Right, but the cars that are scanning signs and will have the ability to read said code are the ones being suggested that they should consult this database to avoid errors. If they're consulting it to avoid errors, they could just use it directly

Now you have two sources of truth for autonomous and non-autonomous cars. You end up with two groups playing the same game by different rules on the same board simultaneously.

Whether or not that's a problem in practice is not clear to me. Among others, taxis, construction vehicles, emergency vehicles, garbage and delivery trucks, municipal busses, school buses, bicycles, motorcycles, and vehicles in funeral processions all play by different rules than the average motorist.

This mostly doesn't cause disasters. Of course they're visibly different for the most part and make up a comparatively small percentage of traffic.

Ride hailing vehicles might be an interesting point of comparison: they're visibly similar to normal vehicles, comparatively common, and play by something resembling taxi rules.

honestly if we're going this far we may as well embed a speed system in the road itself and have the signs for redundancy.

I can see potential problems with temporary signs, such as those put up for road works, around accidents or for police enforcement.

That's why we need to sign the signs.

And use a blockchain to track every interaction between passing cars and the sign. Which makes speeding tickets all that easier.

https://xkcd.com/1958/

Signs are already reflective and pretty standardized. I don't think machine-readable codes are really necessary for this.

One advantage of something machine-readable, like a QR code, would be to incorporate additional information (more than could be easily consumed by a human).

For example, a speed limit sign could include the name of the road it controls, which would help reduce instances of cars suddenly slowing to 35 mph on the freeway when passing a sign on the frontage road.

It might also be useful for cases of (this is US-centric) yellow "advisory" speeds posted for, e.g., sharp curves. The machine-readable aspect might indicate how long the advisory speed applies (next 1000 ft) and why (sharp curve, hidden intersection, etc.)

If you just want to feed computers just put a database with every sign location and data.

That way even faking or destroying sign would be ineffective.

Would have to be updated during temporary situations (roadwork etc) tho

> That way even faking or destroying sign would be ineffective

In theory you could add an HMAC (or similar) signature to the QR code. It would be bigger, but if cars maintained a DB of state DOT public keys, you could mitigate this somewhat.

Then you’d also have to worry about duplicate codes, but at least they wouldn’t be “fake”. Maybe even add lat/long coordinates to the code… again, more data, more pixels required, but it would make sure the signs are roughly in the right place. Which doesn’t seem all that feasible to require construction crews to put the right sign in the right place.

Logistically this doesn’t seem all that promising.

Just give the road crew a phone app that can read the sign.

Given the phone's camera, compass and GPS, validating that the sign has been installed as specified (location, facing direction) is almost trivial.

We can barely just keep a road painted. There’s no budget for wholesale replacement of signs, which often have replacement spans in terms of decades.

Or they could have something like an IR beacon, that way cars can recognize them without relying on computer vision and nothing that looks like a road sign can confuse the system.

They have specific shapes and colors, which probably work the same way

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