Gargoyle, your explanation, that the expansion has somehow been controlled or diverted into a widthways expansion which doesnt cause a problem seems a bit incomprehensible to me.I dont see how you could make a bit of metal expand sidewsys but not lengthways(not that I'm any knd of metallurgist).
   There is another explanation in the papers today.It says the new=style long rails were of a different kind of steel, and were somehow"set" or "solidified" or whatever at an appropriate temperature that was average for the expected climtic conditions.The result being that they would only contract a little bit in extreme cold, and only expand a little bit in a heat wave. I can sort of understand that, except that temperature extremes in Germany and France(with their more continental climate) are wider than in England. Yet these wily foreigners dont seem to be having the same problem. Maybe they use a different kind of steel?
    Anyway, it's all quite amusing, and to the old favourites of the wrong kind of snow and the wrong kind of leaves, we can now add heat as the thing that catches us unawares.
    And to digress, to the "wrong kind of leaves". It's a funny thing, but if you're boating, leaves can stick to the propellor and form a great mass which slows you down. You'ld think they'd fly away from a moving prop, but surprisingly thet are drwan towards it. And the inriguing thing is, oak leaves are the worst offenders(I have oftten observed this). I presume it is because the scalloped edges make them more able to interlock and form the solid mass that coats the prop. Interesting, huh?
   (this has already been mentioned above): just to expain to non-British readers: the reason I called this thread the "wrong kind of heat" is that many years ago bad winter weather caued train delays, and a luckless British Rail spokesman blamed the delays on the "wrong kind of snow". This has resulted in derision for the railways ever since, and any reason for delay is lampooned by variants of the "wrong kind of" phrase.I got in first yesterday, but a glance at today's English newspapers shows all the articles deploying phrases like "wrong kind of heat" or "wrong kind of summer". It has become an ongoing folk-joke.