Currently on Arstechnica there is a 7-8 page thread talking about a recent accident involving a Model S that rear ended another vehicle while driving down I5. The driver didn't realize that she had turned off the adaptive cruise control, and assumed that the car would stop. The car didn't stop because the driver had disabled TACC by braking. My initial conclusion that while it was the drivers fault it was also a UI issue because the car was in a different mode of operation than what the driver expected. In mulling it over the last day and half I've come to two conclusions that are related. 1.) There seems to be a lot of confusion among everyone in that thread over what constitutes Automatic Emergency braking. There were lots of assumptions that the automatic emergency braking should have stopped the car regardless of whether the driver hit the brakes or not. But, they didn't seem to realize that the Emergency braking on the Tesla is only designed to reduce the severity of the crash. It's designed to only activate when a crash is determined to be unavoidable. At least that's what the user manual states. In researching it a bit I realized the entire industry didn't have a standard as to what emergency braking was. The Insurance institute's best rating doesn't even require a car to stop all the way. It's simply a rating of cars that have automatic braking systems that can reduce the severity of a crash. Yet, lots of companies use the verbiage of accident avoidance. 2.) That adaptive cruise control systems are inherently incompatible with automatic emergency braking systems that only offer crash mitigation. The problem is the mode of operation for TACC allows a driver to comfortably expect the car to stop for upcoming traffic. Over thousands of miles the driver gains a good level of confidence in it, and there is little concern about it stopping. But, if the user has accidentally disabled the TACC it means the driver is unknowingly relying solely on the emergency braking to save his/her bacon. But, the emergency braking is only designed to reduce the severity. It's also designed to be easily disabled by hitting and releasing the brakes.