BMW handles it if the navigation database is up to date. At least on the A2 in the Netherlands, which has the 06:00 to 19:00 changes between 100 and 130. It also understands temporary changes for roadworks, but gets it wrong when a roadwork/temporary sign has an exception like "when road is wet"
That tells me the camera only understands the main sign and then the navigation database tells it about exceptions / special cases. Nice as a small reminder on your screen, but I wouldn't trust it to self drive based on that data.
In the UK smart motorways can vary from 30mph to 70mph according to traffic. This can change within minutes and obviously cannot be in databases. So this is a good case for sign recognition. In theory though, there is some network that's updating the speed limits and there's no technical reason why that couldn't be a public information service (maybe it already is).
Then you have the sibling comments - speed limits which are time based. I would imagine this is country specific and is, mostly, a matter of public record. But would you trust CV to recognise text on a sign with specific hours? I don't know how complex the signage is, but trying to use ML for this seems absurdly wasteful of resources.
Finally you have other information - how fast are the cars around you travelling? Have you detected an obstruction on the road (eg cones)? Is the weather inclement and therefore you should drive more slowly, etc.
I would imaging that if self driving cars become ubiquitous there will eventually be a system for real time speed limit determination, whether that's some kind of wireless beacon at regular intervals or an online database that's kept up to date I don't know.
For the car to react according to how other cars drive, you need to have other cars on the road at the same time. I have a narrow gravel road where the limit is 30km/h but safe driving is between 10 and 20, but my car tell the limit is 50km/h. It can be weeks without me seeing other cars on that road at the same time as me. Some mornings during the winter I can drive because I know where the road is, not because all of it is visible. Good luck having an autopilot doing that
Similarly the car should be able to identify road surface conditions and also how much power it's needing to put in to achieve a set speed. If it's identified that traction is being lost over gravel, then it should reduce power.
Equally the autopilot should consider visibility. There are plenty of roads that are national speed limit and you'd be insane to drive at 60 on them due to blind or extremely tight corners.
But with LEDs this seems like massively over-engineering the problem. Why use computer vision when you can potentially broker a deal with the highways agency to get live speed limits on a particular stretch of highway?
Current Teslas CANNOT have this error simply because MobilEye patented reading speed limit signs and Tesla no longer uses the MobilEye system and haven't since mid-2016.
Road construction, for example is a reason why
Roadworks are an obvious situation where you drive at a _lower_ speed. This would be a case where you could use computer vision to identity an obstruction, identify roadworks and then adjust speed.
Those databases shouldn't be out of date. Most highway agencies (UK for sure) publish planned works and improvements weeks in advance. Google and Apple both show road closures for example. I belive speed changes are similar.
This is literally Google's back yard
This shouldn’t be a problem, in general, with a couple extra sanity checks.
I would expect the correct solution to more commonly have the opposite problem: too slow in a faster zone.
You perform the task of vision 100% of the time driving. From a purely probabilistic standpoint, even assuming highly accurate ML, the relatively infrequent database updates still make for a sensible prior.
This is somewhat adjacent to what Gary Marcus has been arguing, and I think it makes a lot of sense; there seems to be no compelling reason to rely exclusively on primitives (i.e. vision) when good priors are easily accessible.
But a car thinking a 35mph zone is an 85mph zone... that could be a very big deal indeed.
Regardless, if self-driving cars (or at least "computer assisted driving" cars) were to be widely deployed enough and shown to depend on these sorts of databases, I'd expect it to become a legal requirement to make sure these databases are kept up to date by city/county/state agencies, and that car systems get those updates. Otherwise, expensive liability ensues.