Is that how speed limits work in the US? It’s my understanding (elsewhere) that the limit is in enforcement after you past the sign, not at some unspecified distance before it, or when you see it. The sign itself is the only transition point between limits.

Yes that is the way it works in the US, but as a practical matter most people start speeding up as soon as the higher speed limit sign comes into view. And of course conversely they don't start slowing down until they pass the sign posting the slower limit.

Right, but both those things would elsewhere (I’m thinking of the UK) be considered bad driving and you could (and people do) get speeding tickets for this.

I’d expect a self driving car to be more aware of the rules and drive according to the law.

I was going to post that!

What are “reasonable” rules for autonomous vehicles? Should they stick to the limit literally, so only start accelerating after the increased limit sign? (There will need to be warning signs when a speed limit reduction is ahead to give the vehicle time to comply.)

Would a vehicle speeding up before the sign indicate a failure or error in the system?

It's important to follow the average speed of the traffic you are in, if you keep to the speed limit while driving slower than the average your driving causes a danger on the road by causing people to drive around you and changing lanes and speeds is where accidents happen.

The slow driver isn’t creating the danger though. It’s all the drivers going over that actually create the danger you describe. If everyone just followed the laws, the danger you describe would no longer exist. Normalization if traffic violations is compounding the problem of the danger we face on the roads. So many problems could be solved and so many lives saved if people just followed the laws. The fact that everyone isn’t following the laws doesn’t need to be accepted as status quo.

> The fact that everyone isn’t following the laws doesn’t need to be accepted as status quo.

It literally is the status quo. If I were still working on autonomous cars, I'd be much more inclined to work into the true status quo rather than imagine the status quo ought to be different and build towards that.

The status quo is also that people don't pay attention and are rude to pedestrians/cyclists/each other and ignore rules all the time (ever try waiting at an unsignalled crosswalk on a busy 4 lane road?). The one thing that I can't wait for is traffic enforcement by autonomous vehicles.

In Arizona, it is not against the law to drive over the speed limit. But it is against the law to speed, or drive too fast for the given conditions. Driving over the limit is evidence that you might be speeding. If everyone else is driving above the limit, and you aren't, you are the one causing the danger.

Your description does not seem to be consistent with my reading of the laws that are referenced from this page: http://azbikelaw.org/speed-limit/

I suspect that the 35 mph reports came from the other side of the street.

On the northbound side it changes from 35 mph to 45 mph right after the bridge just before the freeway. Southbound, it changes from 45 mph to 35 mph about 140 feet after Washington St, well before the freeway and bridge, and about 150 ft north of where the accident occurred.

If someone near the scene wanted to find the speed limit, and failed to consider that the two directions might have different speeds, I'd expect them to be more likely to find the southbound speed. That's because it is common to place speed limit signs shortly after intersections so that people turning onto the road won't have to go long to find out the correct speed limit. So I'd expect them to head toward the Washington/Mill intersection to start searching for a speed limit sign.

For the curious, here is the accident location on Google street view [1]. Back up 17 steps from that, continuing to face north, if you want to see the applicable speed limit sign. Or cross to the other side from the accident location and go north 8 steps to find the speed limit for the southbound road (it's on the last street light before you reach the intersection).

[1] https://www.google.com/maps/@33.4363673,-111.9425082,3a,75y,...

The accident was ~590ft after the speed increase.

So about 6-8 seconds or so, as the car was still accelerating most likely. There is also probably a slight delay for AI based driving after speed limits change, so probably closer to 4-5 seconds later.

That actually sounds like a potential corner case - braking while still accelerating. I'd hope to all that's holy that sort of corner case comes up in your first million miles of testing and not basically in production, but it sets my debugging nose a-twitching.