This sort of came up in another thread, but temperature compensation would seem to be a real issue in places with wide extremes, and should be an item of interest if "global warming" ever becomes local (one might wonder with this year's winter-spring in CA - snow expected at Tahoe on June 1).

For trolley wire/catenary: Sacramento RT uses the constant-tension counterweighted variety for most of it's PRW lines and some in-street. I've noticed during very hot weather (110+F days, happen occasionally in July-Aug-Sept usually as part of a week or more well over 100) that the stack of weights is often on or nearly on the ground. Especially on days when seen from the bus bridge after a train pulls down the wire around Power Inn (has happened a couple of times). Maybe they should cut a slot in the pole base and drill a hole in the ground for the weights to drop further? But on winter days near 20F (also not uncommon at 0530) the stack is nearly at the top of the pole. Do they have to string wire at a particular temp to make it all work? And for those spots where the weights hit the ground presumably they should reduce the length of wire being tensioned by adding more weights elsewhere?

For welded rail: similar issue. I've heard of "sun kinks", and many RRs slow down on really hot days (though for LR it might just be that the substations are overloading with all the trains cranking the a/c) perhaps to provide a little extra margin for stopping in case a kink appears. Does welded rail have to be laid at a particular temp say near the middle of the expected range to make things work or are there ways to adjust it afterward? Are "sun kinks" something only found with welded rail? Perhaps the old jointed stuff was loose enough to absorb the expansion, but with all the joints it would seem easier kink it too.

Thanks for any comments from the experts we seem to have here!