Can we extend the question beyond the U.S.? What are the high/low speed limits in your country?
U.K. = 70mph/20mph (that I’ve seen)
South Africa = 120kph/30kph (roughly 75 and 19 mph)
Grim
Wow! My freakin NEON, non-turbo, went 120! WOOOHOOO! I BEAT MUSCLE CARS! ('course, i’d never try it with my new car, a Kia Rio, and the wacking my Neon took made me sell it at 75K.)
[WAG]
I think the reason for these “oddball” numbers is that when people see a sign that says “speed limit 10” they are apt to fudge a little and think “ah hell, I can probably go 15 through here and nobody will care.” When an exact number is used, however, people are more likely to pay attention to it and obey it. The other day I saw a posted speed limit of 11 mph in a park.
[/WAG]
In Idaho for regular cars the speed limit on Interstate highways is 75 mph except for urbanized areas where the speed drops to 65. Of course a lot of people still drive 75 anyway. On non-Interstate highways the highest limit is 65.
On the 405 (San Diego Freeway), near Carson, there is a weigh station for trucks which sports a sign bearing “Trucks 3 mph”. I don’t know if that would really count as the lowest limit, though.
The parking lot I often frequent in Toronto has the oddball limit of 11 kph.