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Comment by sweden | Hacker News Reader

It is mentioned in the manual of the car:

"Traffic-Aware Cruise Control cannot detect all objects and may not brake/decelerate for stationary vehicles, especially in situations when you are driving over 50 mph (80 km/h) and a vehicle you are following moves out of your driving path and a stationary vehicle or object is in front of you instead."

You can also read here that Volvo's system faces the same problem: https://www.wired.com/story/tesla-autopilot-why-crash-radar/

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This is not a RADAR problem, it’s a world modeling problem.

So you’re sending out pulses and listening for echos, which tells you how far away something is in a particular direction. You correlate subsequent pulses to say whether the object is moving toward you or away. If you have a car 50 m ahead of you every time you ping, everything is good. Now that car suddenly swerves around a car stopped in front of it, and your ping off that object says 60 m. A crash is less likely, your model thinks! The object in front of you is rapidly speeding away! By the time it realizes it isn’t, boom, crash.

That’s not how it works in my limited understanding. Radars don’t just detect the positions of object, but also their relative speed. For this, they take advantage of the Doppler effect. When a pulse gets reflected, its frequency rises if the object is moving towards the radar, and falls if it’s moving away.

You could be right, either in this case or other cases. I'm entirely inferring what autos are doing based on their failure case (not detecting stationary cars when the car in front of you swerves around them); that sounds a helluva lot like mistaking the new car for the old.

Again, not saying it's a limitation of RADAR; it sounds like a deficiency in the way they're using it.

Although there's an inherent trade-off between detecting position and speed. Longer pulses give more accurate frequency/speed detection, while short pulses give more accurate time/position detection. This is the same phenomenon that underlies Heisenberg uncertainty.

IIRC the radar can detect the object but it has too many false positives, like a small soda can that has a lucky alienation and shape that make it appear as a big object. So the system ignores the static signals of the radar, because randomly stopping each time an small object is confused with a big object is also dangerous. And the system uses other signals to identify and avoid static objects.

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