From: rcp27g@gmail.com   
      
   On 2015-02-15 05:32:20 +0000, peterwezeman@hotmail.com said:   
      
   > On Friday, February 13, 2015 at 2:56:43 PM UTC-6, hanc...@bbs.cpcn.com wrote:   
   >> On Thursday, February 12, 2015 at 1:02:46 PM UTC-5,   
   >> peterw...@hotmail.com wrote:   
   >>   
   >>> 1. In designing the iconic FT freight locomotive and E series passenger   
   >>> locomotives, Electromotive put a hood-like structure on the front   
   >>> specifically to give some protection to the engineer and fireman in the   
   >>> event of a collision at a grade crossing, and virtually all subsequent   
   >>> American locomotives have continued this practice. Is there any   
   >>> requirement for grade-crossing protection on self-propelled motor unit   
   >>> passenger cars?   
   >>   
   >> Yes, extensive high-strength protection against collisions.   
   >>   
   >>   
   >>> 2. In the accounts I've read, the lead unit on the Metro North train   
   >>> was set on fire by gasoline from the fuel tank of the Mercedes Benz   
   >>> SUV. Barring the few battery powered cars in service, every vehicle hit   
   >>> at a grade crossing has a fuel tank; in the case of a semi truck there   
   >>> might be as much as three hundred gallons of diesel oil onboard. Does   
   >>> the design of a locomotive or motor unit incorporate any protection   
   >>> from this?   
   >>   
   >> Short of hitting a fuel truck, this kind of fire is unusual in grade   
   >> crossing accidents.  Usually the vehicle is just crushed or pushed   
   >> aside and does not catch fire.   
   >>   
   >>   
   >>   
   >>> With modern welded rail track, broken rails are a known and feared   
   >>> failure mode.>> They are?  I thought welded rail reduced the incidence   
   >>> of broken rails.   
   >>   
   >> Also, I don't believe third rail is welded, plus it is very rare for it   
   >> to break.   
   >>   
   >> In any event, a broken rail would disrupt the signal current, causing   
   >> the block to go red.   
   >   
   > Welded rail is laid down in the warmer part of the year and, when it   
   > gets colder, it is prevented from contracting thermally by a system of   
   > rail anchors clipped to the bottom flange of the rail and bearing   
   > against the ties. In winter, rail can be in a state of tensile stress   
   > of several tens of thousands pounds per square inch.   
      
   Welded rail is laid under tension, with the level of stress in the rail   
   selected so that on the hottest days it will approach zero (welded   
   rails will buckle if they get too hot so that the rail is in   
   compression, the result is a sun kink).  For locations with a high   
   seasonal variation in temperature, the grade of steel used in the rail   
   has to be chosed carefully to accommodate this stress.  It is of course   
   easier to do when the ambient temperature is higher, but machinery   
   exists to allow it to be laid year-round if necessary.   
      
   > In normal use rail is subject to cycles of stress as trains move along   
   > it, and the resulting metal fatigue can result in cracking. If a crack   
   > reaches so-called "Griffith length" when the rail is in tension the   
   > crack becomes self propagating and spreads through the remaining depth   
   > of the rail in a fraction of a second, leaving a dangerous gap in the   
   > broken rail. Railroads employ a variety of magnetic and ultrasonic   
   > scanning machines to detect cracks before they reach Griffith length.   
   > If cracks are found, they are removed by grinding or milling down the   
   > upper bearing surface of the rail, which also serves to restore its   
   > correct profile. I believe that at least occasionally rolling stock has   
   > been impaled by the broken end of a rail.   
      
   The result of not doing this can be seen in the Hatfield crash in 2000.   
      
   Robin   
      
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