No, you&#x27;re missing the physical picture. Someone driving at 30mph over 20mph saves time only linearly, but to maintain that speed, the vehicle has to work much harder as air resistance, the major factor above 15mph, grows with the square.<p>As such, it makes sense to slow cars down to 20, even 15mph - the time loss (if there even is any, people driving in cities are just accelerating unnecessarily from light to light) very much makes up for the dramatic reduction in kinetic energy that endangers pedestrians and other road users.