Jack G. from Florida writes:

"I drive a 2015 Audi S8 and love the car in every manner -- except the CMBS/ACC in it has no guaranteed reliability. I have been in situations in traffic using the Stop & Go ACC system when a car will change lanes out of my path ahead and suddenly, out of nowhere ACC will rocket my car at up to the top speed I had the limiter set at, sending me hurtling toward a car ahead!"

Audi offers a somewhat confusing explanation of this in the official owner's manual, saying the adaptive cruise control is -- and isn't -- suited to use in stop-and-go traffic.

Bottom line, these systems are the early stages of self-driving and, as such, need to be understood before you rely on them. They aren't as simple as past cruise control systems.

Tesla and Mercedes are among the carmakers who have had to revise the way they describe these systems to the broader world and to drivers.

Jack does on to say that his Audi's ACC "did save me on one occasion from a very low-speed collision where I was briefly distracted and the car ahead slammed on brakes -- my car automatically brought itself to a complete stop before my foot could even touch the brake pedal."