Speed of light the "local" speed of light is constant and equal to "c", but the speed of light along a trajectory of finite length can differ from "c", depending on how distances and times are defined. It is generally assumed that fundamental constants such as "c" have the same value throughout spacetime, meaning that they do not depend on location and do not vary with time. However, it has been suggested in various theories that the speed of light may have changed over time. No conclusive evidence for such changes has been found, but they remain the subject of ongoing research. It
Road speed limits in the United Kingdom change in the crash rate on the M6 in Cheshire or on the M1 in Northamptonshire. Although these 70mph speed limit road signs are normally not used on motorways (the National Speed Limit road sign is normally used, as it makes it more understandable for motorists their maximum speed on the type of vehicle they're using), they have been used on non-motorway special roads within the UK, and across the motorways within Scotland. Speed limit enforcement is used to check that road vehicles are complying with the speed limits. Methods used include Fixed speed cameras, Average speed cameras and also