About (E), one thing to keep in mind is that the LSAT always baits you to make assumptions. As much as you can, resist taking the bait and making those assumptions. More people in the car, may not mean that the driver will be distracted and therefore get into accidents more often. Those passengers could be angels. They could even positively help the driver drive better.
More people in the car, however, does mean that there are more people in the car.
Consider the same car that gets into the same fatal accident. In one world, that car has 1 person in it, in another world that car has 5 people in it. Which world do you think the fatality rate would be higher? Of course the car with more people in it.
That’s how (E) weakens the argument without having to assume anything.