The rhythm of the railsJONATHAN HAYWARD/The Canadian Press
Welcome to the Collected Wisdom Express, the fastest train in Canada. On a good day, it can make the journey from Toronto to Ottawa in, oh, seven or eight hours.
THE QUESTION: "Before we had welded railway tracks, we used to hear the clickety-clack as the train ran over the gaps in the rails," writes Paul Hallam of Toronto. "We were told the gaps took care of the expansion and contraction of the steel caused by extremes of temperature." With welded joints, he asks, what happens when the steel expands and contracts?
THE ANSWER: Continuous welded rail is laid as much as possible during days of average temperature - in other words, not on very hot or very cold days, writes Eric Wicherts of Calgary, who's a member of the American Association of Railroad Superintendents. He says this limits potential expansion or contraction of the rail. "Secondly, modern fastenings, especially when combined with concrete ties, can withstand the pressures in the welded rail caused by temperature change while still holding the rail firmly in place."
However, Michael McWilliam of Victoria says rails with gaps still have their advantages. Coping with thermal expansion is indeed one of them, he writes, but the real benefit of a gap is that the rest of the rail structure is simpler and cheaper to build since it doesn't require welding.
He says any long, slender beam (such as a rail) can become unstable under thermal expansion. "This instability is referred to as buckling in general, but for rails it is called 'sun kink.' " If the rail has no gaps, he says, the engineers have to assume the railway ties will need to resist a greater buckling force, requiring the track to be built with more expensive ties made from either higher quality wood or concrete.
"Because of their lower costs," he writes, "tracks with gaps are desirable for routes where traffic is light and slow, such as rail yards or loading docks. Yet that clickety-clack will cause wheels and track to wear out early or force trains to run at slower speeds. Thus, for high-traffic routes where speed is important, the extra cost of welded rails is justified."
THE QUESTION: Frank Durante of Edmonton says his daughter would like to know if there's a hierarchy attached to the different coloured hard hats worn by construction crews.
THE ANSWER: "Generally, white appears to indicate managers, supervisors, engineers or architects," writes Carla Hagstrom of Toronto. "Yellow indicates labourers; blue, technical advisers, electricians, plumbers or on-site medical personnel; red, safety inspectors; green, visitors; orange, road-construction or general labourers."
HELP WANTED
- "We have been informed that 80 per cent of Canadians watched part or all of the men's Olympic gold-medal hockey game," writes Colleen McCarthy of Halifax. "How is this calculated?"
- We often hear of someone being put in the "limelight," says Derek Wilson of Port Moody, B.C. What is "limelight"?
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