Anyone driving through Bourton on the Water in the last couple of years will (hopefully) have noticed the ‘new’ 20mph speed limit. Given the large crowds that the village attracts throughout the year and the narrow streets, this seems a perfectly adequate speed.

For those of us who managed to stay awake during our school physics lessons, we may recall that the energy possessed by a moving object (its kinetic energy) varies as the square of the speed at which that object travels. In the context of speed limits, this means that a car travelling at 40mph possesses 4 times the energy of one travelling at 20mph. In the event of a crash, all that energy is lost in the collision causing damage and possible injury.

Air resistance, or drag as it is known, also varies as the square of the speed of the car. Recently, some UK motorways are displaying speed limits of 60mph rather than the usual 70mph with an accompanying variable message sign saying that speed is being limited to ‘improve air quality in the area’. Reducing speed from 70mph to 60mph results in a 27% reduction in drag with an associated reduction in fuel consumption and harmful exhaust emissions. If you live near a motorway such an improvement in air quality must be a step in the right direction.

Looking around the museum it is clear that 20mph zones are nothing new. It is quite easy to spot the 15mph sign in the Mill Gallery and the images below show some of the other signs that may be unfamiliar to today’s younger visitors. If you are visiting the museum, how many more can you spot as you wander around?