There is now a big push to finish installing Positive Train Control   
   passenger routes.   
      
   But what was wrong with the older technology would that automatically   
   stop a train if it passed a red signal or exceeded the speed limit   
   (per signal) for a block?   
      
   It seems the old system did everything we would want.   
      
   Note that this system was installed on the LIRR following several   
   bad accidents, and AFAIK, was successful in safety.   
      
   Further, PATH is a relatively low speed system and is well   
   protected by trip-stops.  Why does it speed expensive PTC?   
      
      
   detailed article describing old system here:   
   https://books.google.com/books?id=0SADAAAAMBAJ&lpg=PA2&dq=popula   
   %20science%20july%201951&pg=PA50#v=onepage&q&f=false   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)