Not rocket science. Multiply posted kph speed limit in your head by 0.6 to convert to approximate conservative equivalent in mph. 20kph=12mph, 40kph=24mph, 60 kph=36mph. 80kph=48mph, 90kph=54mph. Actual speeds convert to 12.43, 24.86, 37.28, 49.71, and 55.92mph.