I have been thinking for some time about the idea that motorway lanes could be used as an analogy for electron energy levels. Slower, lower energy cars in the inside lane and faster higher energy cars in the outside lane. The inside lane should fill up first etc. Then there was the traffic jam. What would that represent? It helped me to realise that the exclusion principle must apply because you cannot put two cars in the same space at the same time which suggests that the cars might be fermions.
