12 20 2014
  11:26 am  
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Once again a heatwave is causing a MAX train slow-down, and The Skanner News asked Angela Murphy at TriMet: What does the weather have to do with the train tracks?

Murphy reports that today – and for any day when the temperatures are over 90 degrees – the MAX trains run 10 mph slower through areas where their usual speeds are above 35

"The slower speeds are necessary to prevent damage to the overhead wire and rails. Expect possible delays of up to 15 minutes," she advised riders this morning.

The impact that hot weather has on the steel rails and power lines is called "sun kink."

This is how TriMet describes it:

"When temperatures along the alignment reach 90 degrees, we reduce the speed of trains by 10 mph in areas above 35 miles per hour. When temperatures along the alignment reach 100 degrees, we reduce the speed of trains to no faster than 35 mph throughout the system.

"These heat related slow orders are put in place as a safety precaution because extreme heat can cause the rails (which are made of steel) and the overhead power wires (which are made of copper) to expand. When it's 100 degrees out, a 1-mile stretch of rail in the MAX system may expand up to a few inches. When it gets too hot it can actually bend or bow outward. Our operators and controllers call this a 'sun kink.'

"The overhead power wires may also expand in the heat. Because copper expands more than steel, and because we can't allow the overhead wires to sag, we have a system of pulleys with counterweights that tug on the wires to keep them tight. Sometimes, it gets so hot that the counterweights touch the ground and the wire starts to sag anyway.

"Our operators have to watch for both sagging power wires and 'sun kinked' rails when it's really hot out. To be safe, they slow down to make sure nothing goes wrong. As it gets hotter, they have to slow down more."

More information on MAX schedules here

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