Queen Tower's last day in use?

I went to visit Queen Saturday afternoon in Plainfield, which was rumoredly "demolished". Do we know when Queen was last used for its built & intended purpose? I've assumed because its in pretty good shape maybe the late 80s, early 90s.

And because if people are interested, the shots from Saturday:

Located just east of the Plainfield station was 'Queen' tower. Named after New Jersey's queen city, Plainfield. The tower controlled the crossovers and the entrance to the small yard.

That tower screams 50's or 60's utilitarian inspired architecture, as plain as any elementary school built in that era. The Blue Comet Website has a pic of it from (I assume) the 70's.
http://www.thebluecomet.com/cnjQueen.jpg
It's almost a dead ringer for the former CNJ STEEL Tower in Bethlehem, which was built in the 50's.
http://www.thebluecomet.com/crSTEELtower.jpg

Fine and dandy, however, when was it last used for the purpose of getting into the yard? (MM/YYYY)
'

I am thinking sometime after 1983 when NJTransit assumed operaions on the line. The towers on the former Erie were in service into 1984/1985 when the Bergen County and Main Lines went to CTC/TCS