Another problem in my opinion is the fact that the metrics in the US are in imperial measures. 30 mph is 50 kph, it's about pure numbers. 50 is higher than 30

Another problem in my opinion is the fact that the metrics in the US are in imperial measures. 30 mph is 50 kph, it's about pure numbers. 50 is higher than 30 so common sense tells you that you are going faster. Even if it is not true. There is a subconscious reaction of people to numbers, no matter the metrics.