there may be an element of over reacting in the UK, but also under design., but the overhead line problem for our railways is that they expand and drop, and then snag and we have seen them occasionally get ripped out by the passing  train. diesels may not solve that. More frequent tension points would, but is not quick.

mike.

there may be an element of over reacting in the UK, but also under design., but the overhead line problem for our railways is that they expand and drop, and then snag and we have seen them occasionally get ripped out by the passing  train. diesels may not solve that. More frequent tension points would, but is not quick.

mike.

Network rail seem to suggest that some of the overheads already have some form of autotensioning on more recently electrified lines (I have no idea about railways but wonder if it's to do with those stacks of concrete slabs hanging on line-ends running over pulleys at some of the stations near me) and it's the older overheads that are more affected.

mapj1: "there may be an element of over reacting in the UK" . When a substantial proportion of the population does not know how to deal with this kind of heat in their place of residence, then "getting the message out" requires grandiose gestures. France didn't react strongly in advance of and during the 2003 heatwave, and as a result suffered some 14,000 deaths due to the heat (some 30,000 across Europe as a whole). 

Brits are notorious (not just via Kipling and Coward) for going "out in the midday sun". Back in 1984, I hiked/ran the Grand Canyon South Rim to North Rim (round about 26 miles) in September. I encountered some young Brits on the trail with half-litre water bottles, convinced they didn't need more - after all, there was a place to refill. You actually need to ingest 1-2 litres/hour minimum in those conditions, depending on what you are doing. I had six litres of bottles with me. That is what I drunk per hour for the first two hours on the way down. 

35° heat here in Bielefeld is often uncomfortable, because it often comes with 60+% humidity. These last few days, we were at about 30%. I was even out riding my bicycle. Lower humidity is more comfortable, but it is however also more dangerous, because you don't notice how much water is evaporating from you. 

Most people I know don't have hygrometers in their houses, but they do know about humidity because you feel it. The good weather services show humidity along with temperature.