on Mon Mar 2 19:01:51 2009, in response to (Photos):R46's coming to pitkin and 207th soon, posted by R32_3671 on Sun Mar 1 19:49:10 2009.
I'm surprised this thread got carried away as far as it did even if it was an experiment. AFAIK, the red threshholad plates indicate that the car has been modified for OPTO by having an ultra sensitive pressure sensor installed which prevents the T/O from getting indication even if something as amall as a cockroach were caught in the door. I'm not sure of this but I think there may be some sort of a door reversing mechanism installed as well but there ia a NYCT CED employee who post here who may have more accurate information as to exactly what the nature of the modification is. In any event, the red threshhold des indicate an OPTO modification which is why it is found on the R-44s and now the 46s since these cars are used in services that operate OPTO. The first cars to get the modification and the red threshholds were the R-68s since they were used on the midnight B shuttle which was the first line to operate OPTO.