When was the Hudson Div reduced from 4 tracks?

Does anyone know when the 3rd and 4th tracks were removed on the Hudson Line, south of Poughkeepsie?

if you believe info from this link http://newhamburg.net/history/page2.htm

granted it doesnt answer when it was reduced from 4, my guess is the late 50's 60s... others for sure will have better links/info than i.

I recall being told that part of the railroad was reduced around 1962-64