I have come to really dislike double alleys feeding a single alley.  The only place I have a double alley that I actually like is a load out that I built that doesn't have the dividing fence.  I have found over the years posting here that my cattle are extremely unique in that the problems that I have with my cattle no one else seems to have, so take my comments for what they are worth.  My cattle will not feed into a double alley at the same time.  Which ever side they start down with the beginning of a new draft they all try to follow the same side.  Instead of having cattle walking down both sides together they will jamb up at the entrance to one side and refuse to go down the second alley.  Then when they get to the front of the double alley the gate seems to invariably be on the wrong side so they just stand there.  I will never go back to a tub, but what I am giving very serious thought to is building a double alley without the center fence that goes down to a single alley.  If I had it to do over, before I would spend the money purchasing another double alley I would have a single alley twice as long.  Either of these options would be better than what I have at the present time.