Actually, the Manual on Uniform Traffic Control Devices (MUTCD) states the following:
Standard: After an engineering study has been made in accordance with established traffic engineering practices, the Speed Limit (R2-1) sign (see Figure 2B-1) shall display the limit established by law, ordinance, regulation, or as adopted by the authorized agency. The speed limits shown shall be in multiples of 10 km/h or 5 mph. http://mutcd.fhwa.dot.gov/HTM/2003/part2/part2b1.htm As you can see, the standard is "multiples of 10 km/h" for American roads. I'm not sure what others do around the world but I do believe that multiples of 5 km/h may be used and sometimes other odd multiples as well. Phil -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bill Potts Sent: Tuesday, March 30, 2004 1:29 PM To: U.S. Metric Association Subject: [USMA:29372] RE: Canadian metric muddle evident Richard Kim wrote: "Ironically, no one complained when we increased the speed limits from 55 mph (88.5 kph)!" Two things about that. First the symbol for kilometers per hour is km/h, as correctly shown on the inner scale of almost all U.S. speedometers. The letter p is the symbol for the prefix, "peta," which would make kph the non-SI value, "kilopetahours." Second, conversion of speed limits to SI would never be as precise as the value you indicate -- although I realize that you almost certainly wouldn't recommend the use of 88.5 km/h signs (as opposed to the more rational 90 km/h). I'd like to see 55 mph, 60 mph, 65 mph, 70 mph and 75 mph replaced by 90 km/h, 100 km/h, 110 km/h, 120 km/h and 130 km/h, respectively. If those states who now have a 75 mph top speed limit don't like 130 km/h, they can always opt for 120 km/h. (Interestingly, in Germany, 130 km/h is considered the appropriate speed [Richtgeschwindigkeit] for the Autobahns. However, on those stretches where speed limits are posted, anything over 120 km/h is rare.) Having said all that, let me be the first to welcome you to the USMA list. Bill Potts, CMS Roseville, CA http://metric1.org [SI Navigator]
