Why is the assumption always made that speed is the major issue? More important issues are:
1. lack of driver priority putting driving and safety above: cell phones, eating, chatting in car, applying makeup, etc
2. lack of driver skills in vehicle handing. How many drivers could be pop quizzed on their planned escape route for an accordian pileup in the last 3 minutes?
3. lack of driver skill enhancement. Collisions are explained away as accidents and not as driving errors with corrective education needed. Imagine a world where after each collision, each driver had to complete 15 hours of classroom instruction and 10 hours of in-vehicle vehicle handling course work.
Speed limits have no correlation to safety at all. Professional drivers can maintain speed above 200 mph for hours without a problem. On interstates, you can safely drive a range of speeds from 5 to 140 mph, depending on if you're in prime time rush hour or out in Nevada or Montana in the middle of nowhere.
Speed limits should be totally situational. For example, in a subdivision it might be safe to drive at 40mph with wide visible streets and no humans or animals about. And yet in the same subdivision, add a person walking a dog, a couple out for a stroll, a youngster biking. Suddenly 15mph is too fast. In those conditions the "safe legal speed" of 25 is too fast and unsafe.
Currently speed limits are primarily about providing regular governmental income streams and have no known correlation to public safety. The fallacy that speed kills is just as bad as the fallacy that heart attacks are number one killer. Look at the health data, it's number one killer of the retired simply because when someone passes in a nursery home, something has to be entered as the cause of death. Accidents and cancer are the number one in post-retirement ages.
Speed is a factor, but only for one factor. Biggest factor is dumming down of driver education and vehicle handling skills. If we were really concerned about safety, there would be a higher emphasis put on driver training, retraining and reeducation whenever there is a collision event.