...is how Montana speed limit signs looked between 1995-1999, after federal speed limits were abolished. With this policy, traffic accidents were at a modern low. The average vehicle speed didn't increase much, but the attitude of the drivers towards safety improved. No worries about outrageous traffic cops who will ticket you not because you were traveling at an unsafe speed, but because the county government needs money. And then when the speed limits were reinstituted in 1999, the accident rate more than doubled.
Counterpoint: Montana is a wide open space with nothing to hit, and the number of accidents over this time period is statistically small. Accident rates might be expected to increase due to confusion after such a drastic reversion in 1999.
Countercounterpoint: Most states increased the speed limit after the 55 mph limit was abolished, and in general accident rates decreased or stayed constant, contrary to doomsayers' predictions.
I'm not really sure if this is accurate, but I've heard that modern engines actually perform more efficiently at >55 mph, and so the fuel saving argument is also not necessarily valid.
So basically, bring on the autobahn. Also, the advent of self-driving cars may necessitate a complete overhaul of traffic law and infrastructure, so all this may be irrelevant in the near future.
Massive bias warning: I have few statistics to back up my claims. I hate speed limits. I hate cops. I had to wake up at 6 AM to drive to traffic court two weeks ago. Bah humbug.