When they lay tracks, they try to lay them during the hottest time of the year so they'll be at maximum expansion.

Alternatively, rather than right angle cross-cuts they can do the acute slip-cut that allows the tracks to slip by each other --I think the main drawback is wear with these expansion joints.

The normal gapped joints lead to the clickity-clank and also have an issue with compaction of the railbed.

They also expand the rail with thermite which is probably hotter than the sun is going to make the earth.

https://www.youtube.com/watch?v=zqmOSMAtadc

> When they lay tracks, they try to lay them during the hottest time of the year so they'll be at maximum expansion.

The problem is that the planet gets ever hotter and so the temperatures of 20 years ago (or more) are far below today's averages.