From: stephen@sprunk.org   
      
   On 08-Feb-16 20:04, Clark F Morris wrote:   
   > Michael Finfer  wrote:   
   >> As for PTC, there's no reason for it to degrade on time   
   >> performance. The schedules will have to be lengthened.  That's   
   >> something that NJ Transit excels at.   
   >   
   > At least on the corridor since NJT and AMTRAK are going from one   
   > form of automatic train stop with cab signals to a more sophisticated   
   > form, why should there be any need for lengthening schedules?   
      
   Because that's not what's actually happening.   
      
   PRR cab signals were advisory and had _serious_ limitations that an   
   engineer could understand and compensate for.  ACSES enforcement does   
   not do such compensation, which means lower speeds in general.   
      
   The main exception is where cab signals were lowered in the past in a   
   crude form of civil speed restriction, and ACSES separately enforcing   
   the latter (and with far better granularity) allows returning the cab   
   signals to their proper speeds.  There are similar problems with   
   high-speed switches.   
      
   For instance, a long 125mph block with a short 90mph curve might have   
   its cab signals artificially limited to 45mph.  ACSES can enforce 90mph   
   for just the curve, so trains can return to 125mph as soon as they exit   
   it rather than waiting until they reach the next block.   
      
   While not not part of ACSES per se, at the same time Amtrak inserted   
   several new speed codes between 45mph and 125mph, so what used to be a   
   45mph block might now be a 60mph, 80mph or 100mph one.  This allows   
   shorter blocks, which means higher speeds and lower headways without   
   compromising safety.   
      
   > Does anyone know if in Europe implementation of ERTMS level 2 has   
   > degraded line capacity or required lengthening schedules?   
      
   AFAICT, no; even their old systems (developed decades ago) were far   
   better than PRR/ACSES, and ETCS2 is a step up from there.   
      
   ETCS1 would have been a step down in many cases, which is why most   
   countries skipped it entirely, but it's still a better (and cheaper)   
   system than PRR/ACSES, and it's certainly better than nothing at all.   
      
   US freight operators are trying--and failing--to develop systems even   
   more complex (yet less capable) than ETCS3, which even the Europeans   
   have passed on so far despite far more experience/skill.   
      
   S   
      
   --   
   Stephen Sprunk         "God does not play dice."  --Albert Einstein   
   CCIE #3723         "God is an inveterate gambler, and He throws the   
   K5SSS        dice at every possible opportunity." --Stephen Hawking   
      
   --- SoupGate/W32 v1.03   
    * Origin: LiveWire BBS -=*=- UseNet FTN Gateway (1:2320/1)