Defining Renault's Twizy isn't easy. It has four wheels - but isn't really a car. There's space for two - but only one front seat. There's a roof - but it's open at the sides. And it'll match the flow of traffic - but won't use an engine to do so. This is Renault's electric technology at its most extreme, offering perhaps the ultimate answer for city motoring. Perhaps even the kind of second car that all future families should have.