Sliding Patio Doors- what Db level for glass specification

[para1020]

I'm having a 4 door Patio Sliding door set of overall 7m x 2.1m fitted in new extension. Approx. 75m from the doors is a relatively busy urban road. After trawling the internet and speaking to various door manufacturers about suitable sound insulating performance for the glass I'm more confused that ever!. I have one manufacturer offering two options 35db(rw) and 39db (rw) but advised the human ear cant tell the difference these two!. Anybody out there who could offer some advice on the db performance of the glass I should be looking for.

 

[Gazman16]

Those db reductions are equivalent to someone whispering or leafs rustling in a tree, Not worth it for the cost.
Thick curtains or secondary glazing with a 100mm air gap are your best bets.