How many times do motorways cross

Now here is a simple question for you. How many times do motorways speed above boats on the Thames. So do you know your River Thames crossings?
The answer is four. 
The M3 crosses at Chertsey. The M4 near Maidenhead and the M25 crosses the river twice.  Once at Runnymede and again at the QE2 Bridge well out in the east of London.
On Saturday and Sunday Hallmark went under the M25 at Runnymede.  The crossing here is actually two bridges. Both carry the M25 and the A30.
The M25 Runnymede Bridge was constructed when the motorway was built. It sits alongside and complements an earlier bridge built in 1951 by Sir Edwin Lutyens.