It is so important to do the whole trip because switching costs for the driver from "totally inattentive" to "grasping the wheel and driving" are measured in seconds.
Do you assume that the car, after recognizing that human intervention is required, continues to move forward into the path of danger while it waits for the human to take over?
Volvo takes the position for their 2017 that they cannot demand that the driver take over. The car can ask, but must be prepared to pull over and stop if the driver doesn't push the "Manual Drive" button.
Here's the first of 100 self-driving cars Volvo will put in customer hands in 2017.[1] This shows close-ups of all the sensors - high radar and camera behind the windscreen, low LIDAR and camera in the nose, and side and down-looking cameras on the door mirrors. No high-mounted LIDAR, though. These vehicles are intended for self-driving in all weather conditions in Gothenburg, Sweden.
NHTSA levels: [1] Level 3: "Vehicles at this level of automation enable the driver to cede full control of all safety-critical functions under certain traffic or environmental conditions and in those conditions to rely heavily on the vehicle to monitor for changes in those conditions requiring transition back to driver control. The driver is expected to be available for occasional control, but with sufficiently comfortable transition time. The Google car is an example of limited self-driving automation."
Tesla's old system was Level 2. Google and Volvo have level 3 in test. Tesla's new system is supposed to be Level 3. There's a bright line between level 2 and 3 - NHTSA says that at Level 3 and above, the manufacturer is responsible for accidents and cannot blame the driver.