That's a lot of text for explaining why a car might go to 3mph too fast.
There is a big difference between a cruise control and an autonomous car.
In Germany you can get a ticket for going more than 3km/h (1.875 mph) too fast. It's not acceptable for a self driving car to go so fast that you can get a ticket. If that means going up to 6mph too slow, I guess that's the way it is.
Also, going 5km/h means you will need an extra 5m of braking distance or so in case of emergency braking.
With electric cars, regulating the speed smoothly will be even easier.
It sounds like cruise control is dangerous to use in Germany, based on your description. My 2012 VW GLI certainly did not stay within 3km/h of the set speed when utilizing cruise control.
>If that means going up to 6mph too slow, I guess that's the way it is.
If you want to be in a situation that is more dangerous than going 3mph over the limit, sure. If everyone was going 6mph under the limit this would be fine, but staying closer to the speed of traffic around you is less likely to cause accidents than going significantly slower. (Which, surely, if 3mph is significant, than 6mph is even more so)
>With electric cars, regulating the speed smoothly will be even easier.
I agree here. That just means solving the speed determination issue, which is not simple. GPS is the best method we have now, but is very problematic if there is no signal, or a degraded signal.
This would seem like a major problem then. In Silicon Valley it’s very common for freeway traffic to move at speeds that are 10 or 20 mph above posted limits. You either stay under the limit creating a dangerous situation as the result of differential speed or violate the limit and match the speed of surrounding traffic. How does the engineer not become liable in this context, like the VW engineers in the emissions scandle.
> It sounds like cruise control is dangerous to use in Germany, based on your description. My 2012 VW GLI certainly did not stay within 3km/h of the set speed when utilizing cruise control.
You don't need to stay within 3km/h of the speed limit to follow the law. You need to stay below 3km/h over the speed limit. So if your cruise control has a variance of 5km/h, you should set your cruise control at 2km/h below the speed limit.
> If you want to be in a situation that is more dangerous than going 3mph over the limit, sure. If everyone was going 6mph under the limit this would be fine, but staying closer to the speed of traffic around you is less likely to cause accidents than going significantly slower.
Unless your cruise control has a significantly larger variance than all of the other vehicles, you should be fine because everyone else should be setting their cruise control to roughly the same thing as you.
Sounds like maybe the culture is different in Germany for this. In the states 5 mph over the speed limit is normal. While you could get a ticket for it, you won't unless you're in a small town that's just trying to pad its budget. In some parts of the states even 10 mph over is regularly tolerated on highways.
I read your comment and thought that was a ridiculously tight margin of error, even for the Germans. Then I looked up the fine.
€15 for an in-town violation, €10 for out-of-town, no points for less than a 20 km/h variation? That's more of a secret tax than an actual deterrent.
Electric cars can't regulate the speed more smoothly than gas cars while on cruise control. It's about the control algorithms, not the source of power, and the gas systems could be on tighter control ranges if it weren't so inefficient and uncomfortable for the passengers. Adaptive cruise control runs on a PID loop control scheme and overshoot is inherently part of the game.
While on cruise control a car will go slightly faster than the speed setpoint for a few seconds, then slower, then faster, until it settles on exactly the correct speed. Then you go down a hill and it takes a little while to slow down, or you go up a hill and it takes a little while to speed up. Electric cars can use regenerative braking when the car is going down a hill but they're still constrained by the nature of control loops and aggressive braking will just lead to wonky acceleration-braking cycles while hunting for the setpoint.
That's also how humans drive. We just don't do it as well. If you're worried about tickets set your cruise for 3 km/h under the posted speed.
The setpoint is the setpoint. Key element of controls engineering. Secretly subtracting from the setpoint behind the scenes to compensate for your local driving laws would be the car lying to you and just leads to more trouble than it's worth.
Every day people tell me that they want a setpoint to be the temperature that the room never exceeds or the temperature it never falls under or five degrees above the highest temperature the boiler hits. It's like setting your clock ahead by five minutes to avoid being late. You can do it if you want to but it's ridiculous functionality to build into the timepiece.
Further, outside of detection errors like the one in this article, the reaction time of a self-driving car is orders of magnitudes faster than a human. You don't need 5m more braking distance per 5km/h because within milliseconds of the computer noticing the issue the car will hit the brakes. Human reaction time is more like 0.7s to 3s. You still need more time to brake as you go faster but the computer doesn't need as much time as our human laws already give us.
In a case like this where the victim enters the path of the car closer than the car's brakes are capable of stopping, even given instant detection, a human would have just hit the victim at a much faster speed because of the reaction time. That's going to happen sometimes. It's just how it works.
Basically everything you're saying is based on an outdated notion of how cars work and in particular your very German desire to follow the rules exactly. The rules are going to change, dude, and in the meantime you're free to set your cruise at 47 km/h to avoid accidentally triggering a photo-radar trap if you like.
