Is it possible that a room ambient noise generator could reduce traffic sounds from outside?
A white noise generator is like spraying perfume to cover a nasty smell.  The smell is still there, just the perfume is stronger.  The nastier the smell, the stronger the perfume needs to be to cover.

A white noise generator produces noise that our brain quickly ignores.  If this noise is louder that the outside noise, then it will mask it.  But a word of warning, if you have to turn the white noise generator up enough to cover loud outside sounds you might risk your hearing.  Even though our brain doesn't 'hear' the white noise, our ears still do.  And a constant loud noise will produce hearing loss over time.