What makes you think that the autonomous truck will hit the car just like a manned truck? I'd think that with the sensors on the truck tied directly into the autonomous control systems the autotruck could react thousands of times faster and more effectively than a human being truck driver.
Hmm... looks like somebody failed at learning Amdahl's Law.
Let's say a truck is driving at 60 MPH (88 feet per second) when somebody jumps in front of it, 88 feet away. The driver will take 0.5 seconds (44 feet) to react, then the truck's air-brakes will take another 0.5 seconds (44 feet) to engage. By that time, the truck will have hit the person. Then the truck will take another 355 feet to come to a stop.
Let's replace the human-driven truck with an automated one, and assume that the computer is unrealistically perfect and manages to reduce the reaction time to zero (seconds or feet). In that case, it still takes 0.5 seconds (44 feet) for the air brakes to engage, so the truck has "only" 311 feet of braking distance left to travel when it hits the person.
In other words, reaction time accounts for only about 10% of the total stopping distance, so the maximum improvement gained by switching to an autonomous truck would be about 10%. That's not zero, but it's also not "thousands of times" better, as you claimed.