In the Feb 2010 issue of trains magazine; on page 28 it mentions in the second column that the track speed is 70 mph. However; it mentions heat restrictions cut the train speed down to 60 mph till night, and the length of the train reduces the trains speed to 50 mph. Why the heat restrictions and length being an issue on a straight route (braking distance?)?
Heat restriction is due to increased probablity of sun kinks in hot weather. Sun kink is lateral displacement of both rails toward one side or another of the normal line of track. A sun kink is very likely to derail a train.
Mac
Then how come an intermodal train can go 70 mph through the Mojave Desert. Is the speed limit 80 mph?
I’m not sure, but I bet you are on the right track with the speed in the Mojave.
There was a derailment in Attica Indiana a few years back where a long heavy grain train was coming up the spur to reconnect with the main line. The 3 locomotives made it over with only one jumping the tracks. However, as soon as the first hopper hit the sun kink… It was all over. It spilled 82tons of corn, and also clogged up the city drainage system.
Because it might not be hot enough for the heat restriction to kick in. The temperature that will trigger the restriction varies by the location So a subdivision in a normally hot area may have a higher threshold than a subdivision in a normally cold area.
Different railroads have different rules and one company may have different rules for different territories.
Mac
The Mohave thing may have a lot to do with a fairly consistent temperature pattern. Areas with more moderate temps would be more likely to experience an issue with abnormally high temperatures. At least that’s my take…
And, a given track may well have two speed limits - one for pax, one for freight.
Mister Muddy Feathers or Paul should chime in shortly, but basically a section of track will have what could be called a neutral rail temperature, where the iron is neither in compression or tension. Raising the temperature above that temperature will put the rails into compression. Go enough above the neutral rail temperature and the probability of a sun kink gets worrisome. Go enough below the neutral temperature and the probability of a rail break (fracture) likewise becomes worrisome.
The neutral rail temperature in a generally hot area will be set considerably higher than in cooler/colder regions.