The reason for this is everyone is already doing it
Never like when they think that way. Of course no one will exceed the higher speed limit
A lot of people just assume that higher speed limits will make roadways more dangerous, because drivers will exceed whatever ceiling is in place. By the sane token, people think lower speed limits will promote safety by tamping down velocity. But in reality (confirmed by study after
study- PDF) that drivers rarely overshoot their speed comfort zones, even with legal encouragement, and that the perception of hazard on freeways with high speed limits can actually boost safety by heightening drivers’ caution.
The State of Michigan, the MSP in particular, has been THE leader (along with some participation from New Jersey and a few others) in studies on the "85th percentile." The 85th percentile rule holds that 85 percent of drivers are already traveling at the most prudent and safest speed for the current conditions, and is an accepted safe speed that results in fewer accidents. For several years now New Jersey has put this to the test on the Garden State Parkway and on several stretches of the Turnpike where the posted speed limit is variable and changes in real time based in large part on the speed of the 85th percentile. The result has been fewer accidents.
The studies have shown that even if the posted speed limit is 70 MPH, if the prudent and safe speed is 52 (or whatever), that's the speed at which people will drive. The reverse is also true with a posted limit of 55 MPH and a safe and prudent speed might be 65 or 70. The reasoning of "everyone is already doing it" turns out to be sound reasoning. And regardless of the posted speed limit or of the actual speed of the 85th percentile, it's those 15 percent that will be traveling too fast (usually) or too slow for conditions (be those weather or traffic conditions).
Theoretically you could not have any posted speed limits at all (the way Montana and parts of Wyoming and North Dakota used to be) and people would still travel by the 85th percentile rule. The way to ideally do it is more or less they way Jersey is doing it, where instead of hard posted signs of hard limits, you have variable electronic signs that change with the flow of traffic and to let you know that you need to sloe down ahead due to conditions (weather, traffic, accidents, whatever). Michigan will do studies (again, because they've done the same studies many times) to determine which miles of rural Interstate can support the higher limits.
There is no question that higher rates of travel increase traffic related deaths, as most accidents at high speeds tend to be more fatal. But higher speeds don't actually increase the number of accidents. Just the opposite, actually. New York raised the speed limit from 55 to 65 in 1995 and the accident rate has dropped 4% since then. Higher speed limits in California reduced the number of accidents on those roads by 4.6%. New Jersey, Michigan, West Virginia, Tennessee and several other states have the same results. A few years ago when Michigan raised the limit to 70 they haven't experienced any uptick in accidents.
The only study that shows an increase in accidents following an increase in speed limits is the
Iowa study (PDF) where their 1996 increase of the state speed limit from 55 to 65 mph concluded the speed hike caused an eye-popping dramatic jump in both traffic accidents and traffic fatalities. Iowans just can't drive fast. Although, to be fair, accidents and fatalities also increased over the same people in surrounding states that had no speed limit increase, so the speed limit increase in and of itself may or may not be the primary causational factor.
The stretch of the toll SH 130 in Texas where the limit is 85 has resulted in a lower accident and fatality rate (per miles driven) than the rest of the state. At night people tend to travel far slower than the posted 85 MPH, though, likely because the very first night the high-speed section of highway was opened there were four collisions between cars and wild hogs on the road. It's hard enough dodging bacon in the dark at 60 MPH, much less at 85.
