A subway is always a tube, or the underground, or the Metro.
"There's a new picture at the Metro," he said as quietly as he could.
I went down into the Metro and in time arrived at the station.
(Metro de drapo signifus metron, kiu kuŝis sur drapo, aŭ kiu estas uzata por drapo).
(Metro de drapo would mean a yard-measure which was lying on cloth, or which is used for cloth).