Semi-autonomous driving basically blends available technologies, most prominently adaptive cruise control (which uses radar at the front of the car to slow down when the car in front of you slows down) and lane keeping (which uses cameras to spot the lines in the road and adjusts the steering to stay within the lines). Under normal traffic and road conditions, these systems work really well, helping drivers stay straight and keep a safe distance from cars ahead. The system in my Volvo is a godsend on long drives.
But it is important to note that these systems are not perfect, and drivers need to understand what the limitations are. When tested, most semi-autonomous systems don’t react well to stationary objects that suddenly appear; for example, when the car in front of you swerves into a different lane and a parked fire truck looms ahead in the middle of your lane. The computers and sensors in these systems do great at detecting large objects which are moving, but if they break for every stationary object then they wouldn’t function very well. Automakers have to thus find a balance by ignoring objects which are not moving. Hence the issue with a stopped vehicle in front of you.
So while it is easy to get lulled into a false sense of security, drivers have to be smart and know what their cars can and cannot do. Driving in semiautonomous mode means that you should have your hands on the wheel, your feet near the pedals, and be ready to take over in a moment’s notice.
Take the word literally: semi is qualifying the autonomous, putting limits on it. Embrace the technology, just don’t rely on it.