Ultrasonic Sensors in Tesla's Autopilot
I presume it would use delay to determine the distance and frequency shifting due to the doppler effect to determine speed.  The real question is what sort of signal are they using.  Different signals will have different performance characteristics when it comes to extracting propagation delay and doppler shift information.  For example, a short tone of a single frequency works well for measuring the doppler shift, but not so well for determining the delay.  A chirped (frequency swept) pulse works better for determining delay, but doesn't work well for measuring doppler shift.  A randomly modulated pulse works well for both, but requires more signal processing to detect.  I would imagine they're probably using some form of digital modulation (amplitude or phase most likely) with a pseudorandom sequence and then using some digital signal processing to extract the information.