Most accidents that happens in the highways are not because of speeding. You will be more and more alert when you are speeding but for those who follow the rules normally will sleep while driving because its too boring for them to look at the road for hours!! I always do around 200Km/h in the north south highway. I guess there is no point in fixing speed cameras on the highway if the government want to reduce road accidents unless they have other motives. To increase the countries revenue maybe. :)
