Why aren't we using sonar for this sort of thing. Bats have nailed down the echo location thing in extremely heavy bat traffic, but I don't see that being something that has been vigorously pursued by tech companies.
I could also see sonar taking a lot more energy to use all the time as compared to Lidar.
During the time it could take for a sonar (ultrasonic) sensor to send out a pulse and for it to return, the car may have travelled many feet depending on speed and road conditions. This would impact how long it would take to perform an evasive action and return to a safe state.
That is just a guess, though - I haven't run the numbers to know if it is factual. Lidar, though, is much quicker, as you noted.
Looking at Thrun et al.'s paper on Stanley (https://www-cs.stanford.edu/people/dstavens/jfr06/thrun_etal...):
"The effective maximum range at which obstacles can be detected with the laser mapper is approximately 22 m. This range is sufficient for Stanley to reliably avoid obstacles at speeds up to 25 mph. Based on the 2004 Race Course, the development team estimated that Stanley would need to reach speeds of 35 mph in order to successfully complete the challenge. To extend the sensor range enough to allow safe driving at 35 mph, Stanley uses a color camera to find drivable surfaces at ranges exceeding that of the laser analysis."
They built a neural network to analyze terrain and find safe paths- and trained it driving at 25 mph across the environment with the LIDAR providing the control- and then let it work at higher speeds where the LIDAR would be able to panic stop but not much more.
Given that the major players like Waymo/Uber/Apple etc seem to be betting very heavily on LIDAR, one would assume these challenges are being resolved. I suspect the traditionally very high cost of LIDAR was likely a much bigger factor in Tesla's decision not to use, rather than any technical reason. Cameras plus radar is vastly cheaper to ship for now.
Side note: I can't help but be reminded of Napoleon Dynamite's Liger whenever I see Lidar. Makes me smile.
Short version: Regular cars are vulnerable to malicious actors, too, but luckily most people aren't murderers.
2D lidar is less expensive, but still isn't cheap enough for the number of sensors that would be needed (multiple sensors would be needed for proper coverage, if the the sensors were incorporated into the car body); also, they are still mechanically complex (most rely on spinning mirrors or sensors).
That leaves something like flash lidar, which isn't quite cheap enough (though it's dropped in price significantly in recent years), and I think it's resolution is still fairly low - but it does allow for 3D information about the scene, within it's field of view.
I have always understood why Tesla took the route of using cameras only. In theory, it should work fairly well, since humans have been using a similar system for 100+ years for driving automobiles. It really comes down to a software problem (vision and deep learning, etc), more than anything.
Camera sensors are inexpensive, and easy to incorporate into a vehicle. I tend to wonder if maybe augmentation with FLIR and other wavelength sensors might not improve things, but even standalone image sensors - in theory - should be completely workable.
Elon Musk is probably right that in the long term it won't be needed, but those few years count a lot.
0. https://en.wikipedia.org/wiki/Froude_number#Walking_Froude_n...