and the Big Ten used to use it when it has the "Leaders" and "Legends" divisions. In theory the zipper model allows both divisions to have equal representation in a state or region. The lone exception in the ACC is that both divisions don't have equal representation in the state of Virginia. The other possible exception is the New England region if you consider the Syracuse-BC rivalry and assume the Pitt-L'ville pairing represents the Ohio Valley region.

Even though it may not make sense, there is some logic behind why the ACC used the zipper model. One factor is the effort to try to preserve as many rivalries as possible. For example UNC and UVA were placed in the same division because their rivalry is called "The South's Oldest Rivalry" and has been continuously played longer than the SEC's "The Deep South's Oldest Rivalry." Duke and UNC were placed in the same division because of their rivalry (more known for their bball rivalry). The ACC placed FSU and Miami in opposite divisions because they expected the CCG to be a frequent rematch of the regular season game. Clemson and NC State were placed in the same division because of their rivalry (aka the "Textile Bowl" which is a trophy game). Back when the ACC expanded to 12, VT wanted to be in the same division as UVA so that is why they were placed in the same division. Part of the reason is because basketball maintained the same divisions so VT wanted to make sure it got to play UVA twice a year. As a result UMD-UVA were paired up. Clemson and FSU were placed in the same division because at that time the "Bowden Bowl" helped intensify the rivalry between the schools. The 4 NC schools were divided up equally so that both divisions had 1 public and 1 private. The original pairings for the 12 schools looked like this:

Atlantic/Coastal
BC-VT (by default and I think VT's previous AD wanted it)
UMD-UVA
Wake-Duke (NC private school pairing)
NC State-UNC (NC public school pairing)
Clemson-GT
FSU-Miami

When the ACC added Pitt and Syracuse, Syracuse wanted to be in the same division as BC. So the ACC then looked like this:

Atlantic/Coastal
BC-VT
Syracuse-Pitt
UMD-UVA
Wake-Duke
NC State-UNC
Clemson-GT
FSU-Miami

When Maryland left for the Big Ten and the ACC added Louisville, the ACC just simply placed Louisville in Maryland's place as a matter of convenience. So now the ACC has 2 forced pairings (Louisville-UVA and BC-VT) which is not that different than all the SEC's forced pairings (i.e. KY being paired with a MS school, Vandy being paired with the other MS school, TAMU-SC, and I guess even AR-Mizzou). The ACC does have an opportunity to have 7 "natural" pairings, but it would mean realigning the divisions.

BC-Syracuse
Pitt-Louisville
VT-UVA
Wake-Duke
NC State-UNC
Clemson-GT
FSU-Miami

The ACC still has some flexibility on which school ends up in the Atlantic and which school ends up in the Coastal while still preserving the pairings directly above.

The ACC can't go with a North-South alignment because right now it would mean placing 1 NC (Wake) in the North. No way 1 NC school would want to be separated from the other 3. If the ACC expanded to 16 then it could go North-South with the dividing line being the VA-NC border, but that puts the South's Oldest Rivalry in jeopardy of remaining an annual game which the ACC may not want to give up because that is 1 thing it has over the SEC. Making it the only protected cross-division game would create quarks in the future schedule rotation and it probably doesn't make sense to created forced protected pairings for the other 7 members. The ACC can't really go East-West because it has too many rivalries it wants to preserve. Plus, if it did go with East-West, then it would still use a zipper model because all the schools want equal access to the recruiting hotbed states (SC, GA, and FL). The SEC doesn't have to worry about it because it covers the entire Gulf Coast Region which is the #1 recruiting hotbed region.

If the SEC decided to use the zipper model, then it would look like this:

Division A/Division B (based on protected cross-division pairings)
KY-SC
UT-Vandy
UF-UGA
AL-Auburn
Ole Miss-Miss State or Miss State-Ole Miss
LSU-TAMU or TAMU-LSU
Ark-Mizzou or Ark-Mizzou

I think the last 3 pairings has some flexibility on who ends up in which division.
[Post edited by VTHokie2000 at 12/23/2016 9:25PM]