From: ahk@chinet.com   
      
   bob  wrote:   
   >On 2015-02-13 20:23:01 +0000, Marc Van Dyck said:   
   >>rcp27g@gmail.com explained on 13-02-15 :   
      
   >>>or putting in positive singalling control on others (ie where the   
   >>>crossing is protected by railway signals that aren't cleared for the   
   >>>train until the barriers are down and the crossing positively checked   
   >>>to be clear).   
      
   >>This is perfectly feasable but requires to order the gates to go down   
   >>at a distance that is longer than the braking distance of the train.   
   >>This means there will be a long delay between the gate going down and   
   >>the train actually passing the grade crossing.   
      
   >Indeed, this is the case.  It is less convenient but allows for   
   >positive safety.   
      
   >>As it has been mentioned,   
   >>motorists are unpatient creatures; if the delay is too long, people   
   >>think the gates are faulty and start turning around them. You might end   
   >>up this way with a grade crossing that is inherently less safe, because   
   >>of human nature...   
      
   >Solved by making the barriers block the whole road.  As the crossing is   
   >positively checked to ensure the barriers are down and the crossing is   
   >clear before clearing the signals for the trains, the issue of cars   
   >being trapped within the crossing is avoided.   
      
   Clearing level crossings several minutes before the train arrives mitigates   
   against non-existant risk, and it's quite labor intensive. How is the   
   cost of delay justified? How is the personnel cost justified?   
      
   No lives have been saved except during the 5 or 10 seconds before the   
   train arrives.   
      
   >The usual design in the UK, for example, is for the road to be blocked   
   >by four barriers: each covering half the roadway on each side of the   
   >railway.  The warning lights/klaxon start first, then the "entry" side   
   >barriers come down, then the "exit" side barriers come down, then the   
   >klaxon stops (it gets irritating, and once the barriers are down, is   
   >redundant).  Then the crossing is checked to be clear, either by a   
   >person in a local signal box or by CCTV cameras, and if it is clear,   
   >the signals are cleared for the train or trains passing.  It is safe,   
   >but means waits at the crossing can be a couple of minutes before the   
   >train actually arrives.  The crossing sequence is initiated by the   
   >signalman, who can keep the crossing down if there are multiple trains.   
   > They can be annoying, but they are safe.   
      
   I've heard of crossings getting closed five minutes ahead of arrival   
   of the train.   
      
   >Not all crossings in the UK are of this sort, there are also "automatic   
   >half-barrier" crossings that do not block the whole road and are   
   >triggered automatically by the train approaching, without positive   
   >safety, but designed for the minimum road-closed time, so the barriers   
   >come down about 20s before the train arrives.  Such a crossing was   
   >involved in the Ufton Nervet crash, and they are only used on quiet   
   >roads with little traffic, and on railway lines with lower speeds.   
      
   That's common in the US.   
      
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