As a side note, radar in cars and semi trucks are a difficult match. The height of tractor trailer trucks makes it difficult to figure out if they are actually obstacles or if you're really seeing a bridge or something. Normally there's enough hanging down in back that it's not an issue, but in this case the truck was perpendicular to the car. It would not surprise me if the radar went right underneath the truck and either didn't see it, or saw it but thought it was something like a bridge that the car could go under. These are difficult and complex systems to engineer.
I am driving an '14 Audi A6 and I can tell you, the radars + software on it are the most advanced I ever saw. They even catch a small cat when was trying to cross the street. The car actioned a emergency break before I even realized. The only time when this wasn't working, was during a snow blizzard, when the radar sensors got iced and they couldn't see anything. Otherwise, they are pretty wide range, at least 100m.
It also keeps the car in between the lanes - this is done with a camera, but if you take your hands of the wheel, you get a max of about 30 seconds of free driving to maybe open a bottle of water, before it get's really loud.
TIL everyone on Hacker News drives a much nicer car than I do. The crash avoidance measures run in tandem with the autonomous driving features, but the system (which is mainly licensed technology from Mobileye) just doesn't get any depth intelligence from it. Presumably if autonomous driving pointed you into a brick wall, the radar stuff would still trigger the AEB features (autonomous braking).
no such thing exist ...
I suppose I don't really know, but that was Elon's answer to "why didn't the radar see it?"
That's what puzzles me. I don't get how overhead road signs can be a problem, and it couldn't detect something at car height. Its just really odd.