In fact this technology exists and is quite common in higher end vehicles. The terms are Adaptive Cruise Control (keep same distance with the vehicle in front) and Lane Assist (keep the car within the white lines, as long as the curve is <Xdeg). All JLR vehicles have it as option, as do the larger Audis. Even Ford offer it as an option on the Kuga (which is their highend SUV in Europe).

I worked on the systems for both JLR and Ford, the former even have an option where cameras read signposts to adapt the speed (falling back on GPS info if none were visible).