High speed crashes are far deadlier than lowspeed crashes. A car going twice as fast has four times as much kinetic energy to dissipate.
Yet the number of deaths per mile driven fall when all the traffic is going the same speed. That's best achieved by raising the posted speed limit to match a speed that feels natural for that road. I remember someone did a study that concluded New York State's interstates got safer in rural stretches when the speed limit was raised from 55 to 65.
@aspera: You should assign a dollar value to your time and gasoline, and calculate how much of each you spend per mile at various speeds. I ran the numbers for the Subaru, and I concluded the correct speed is around 65mph, but anywhere in the 5575mph range yields almost the same cost per mile.
