 Most of us know that there is a speed limit of 60 km per hour on urban roads. But do you know how this figure of 60 km per hour came up? There are three solid reasons behind this. Reason number one, the stopping distance of vehicles depends on two major factors. The decision making time of the driver and the friction between the tires and the roads. Assuming friction coefficient of 0.4, decision making time of driver as 2.5 seconds, and stopping distance of less than 75 meters, MORDH and that's Ministry of Road Transport and Highways arrives at this figure of 60 km per hour. Reason number two, speed thrills but kills. The injuries, deaths and damages in an accident is directly proportional to the kinetic energy involved. Kinetic energy varies as the square of velocity. That means, if the velocity is twice, damage would be four times. So isn't this a good idea to drive at 60 km per hour rather than 120 km per hour? Reason number three, the air resistance against the vehicle is directly proportional to the square of the velocity. So at higher speeds, the air resistance will be very high, and thereby decreasing the mileage of the vehicle. So 60 km per hour is considered to be an optimum speed for best mileage of your vehicles.