A PCV system ventilates the crankcase at all engine speeds, including idle. The road draft tube only works at speeds above 30 MPH or so because it's necessary to create low air pressure around the bottom of the road draft tube to draw air from the crankcase. If the air inlet for the PCV system comes from the "clean" side of the air filter, engine life is increased noticeably because less dust and dirt is drawn into the crankcase by the incoming ventilation air. That was accomplished on engines with vent slots in the valve cover by welding up the slots and providing ventilating air through a vented, filtered oil fill cap or a tube to the air cleaner from the valve cover.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!