Let me know if I've posted this one before, and if so I'll kill it.
There is a nice, long road in a particular part of the UK which was once in the "open air". One day, the Department of Transport decided that, for the safety of all concerned, the road should go through a tunnel instead. So now one particular section the road, unchanged from its original course, goes through an artificial hill.
Explain, using "yes/no" questions, why they went to all that expense.
"Women who carry a little extra weight tend to live longer than the men who mention it." - Mrs Worrier