My response, (not to displace EOD.....)
The 'speed differential' doesn't cause the accidents. It's the people not paying attention, tailgating, and so on. They have poor driving habits, that may kill them, or others.
(This is one of the favorite arguments of truck drivers when bi-otching about the states with 'split' speed limits....slower for big trucks.)
Like EOD said, higher speeds mean longer reaction times, and longer 'danger interpretation' periods.
(The two cars doing 105 mph in a 55 zone that hit my tractor trailer 14 years ago 'thought' they'd clear my slower moving truck, and din't attempt to slow down until right before impact. At least the SURVIVING driver told the cops that!)
Another favorite argument the truckers like to apply to driving in congested traffic, is "you have to drive like they do', meaning tailgating, speeding, and not letting anybody 'cut in', if you want to make any progress.
That's exactly what I like to see behind me in my rear views! A 40 ton tractor trailer, tailgating, and whipping in and out of traffic like an idiot in a car! On a bike, even a tiny car will be just as deadly if it rear ends me.
Most interstates and limited access highways do have a posted minimum speed limit. (45 seems to stick in my mind) It's rare to see anyone hovering near the minimum, but it happens. It does create chaos, but it's not the fault of the people in compliance with the law.
I saw a large National Guard convoy last week on the interstate. They were doing 50, and stretched for at least a mile. The speed limit in the area was 70. Yeah, a lot of cars approached the tail vehicle at high speeds, even though it was daylight, the hummer had flashing lights, and you could see the slow convoy stretching out in the right lane from a long distance.
Most people aren't capable of driving any vehicle safely at high speeds, or have the judgement to realize when it's not safe
(Example, the morons who barrel through active construction zones with workers, and lane zig zags all over the place.)
If people would drive safely, and use some sense, I could see increased speed limits possible. The problem is, your average driver can't drive safely with the limits where they are, and the speed limits aren't enforced enough, now. You can't force people to have common sense....and you can't teach them to have it.
Some of the laws we have are an attempt to lessen the carnage the dumbarses do.