2 4 6 8 Motorway

The house is clean and tidy, the man from tescos has delivered most of our food and Mrs Dogwood bought the last few bits and bobs from the local supermarket, most of the presents are wrapped and I think we are all set for christmas. The only problem is that the aged ps aren't here yet. They are heading up the motorway from down south, and checking the traffic reports shows a big pile up near Chesterfield, so it's a fair assumption that they are stuck in it somewhere.