It’s a beautiful summer’s day, the sun is shining and the countryside beckons. What better time to open up the garage, spark up the motor of your shiny car and take a leisurely cruise along the highways and byways. But, wait a minute, what’s this? Dirty again? Didn’t you clean it recently, just last weekend? Wouldn’t it be great if your car — or bus, lorry or train — stayed spotlessly clean for a little longer after each wash?