As I am GRR flyer based, I can explain this quite easily. The airport is configured into 2 concourses (A and B) with no inter-connector. Concourse A has Delta, Frontier, Air Canada, & (CO). Concourse B has Allegiant, United, and American (and never a wait)<edit> CO appears to be moved here now.

There are 2 x-ray machines/metal detectors and 1 Nude-O-Scope per concourse, but 1 of those lanes is shared, so there is only 2 lanes to get through. There is no cattle corral to wrap you back and forth so the line can get very long.

The general problem can be explained as too many people for the number of machines. Recently DL moved the LGA and MEM (50 seat CRJ's I believe) direct flights to Concourse B in an attempt to alleviate the problems. The only problem with that is these are the 2 most likely flights to go IROP, which then necessitates re-screening through Concourse A.

Eventually, CO (CO/UA) should move to Concourse B, but in the airports quest to make every $ possible, they want to charge CO more rent/sq. ft. as Concourse B is slightly wider and therefore CO isn't moving until they have to.

TSA doesn't help as they are running the Nude-O-Scope during the peak times and then telling passengers that "it is just as quick as the metal detectors" (it is hard to bite your tongue and not say anything to the smurfs). I had the same morning flight 2 weeks in a row. The first week the wait was 10 minutes (LGA & MEM were still on A), the second week was 50 minutes. It should have been quicker the 2nd week because LGA & MEM were moved to B. TSA seems to be actively pushing some agenda (probably more staffing). On top of that, the TSA director for GRR is also the director for MKG and some other Podunk airport that have very low passenger counts and is applying the same policies to GRR. LAN is controlled out of DTW. As a side note to Gov't efficiency, TSA assigns the number of workers to an airport by the number of passengers that use it, not by the number of passengers it can screen. You will see more smurfs standing around here than any other airport.

The airport recently paid $45k for a consultant to tell them what every FF could have told them; there is not enough security lanes. They are adding a 3rd x-ray/metal detector line to concourse A (which will be another month) , trying to figure out how to make a connector between the concourses, and putting in a Sky Priority line.

They could have taken the $45k, moved CO to B and bought one or several of CVG's fabric covered canopies and connected the two concourses outside. Removing of the gift shop would create room for a combined checkpoint, but according to my sources "isn't ever going to happen".

Adding a Sky Priority lane would make no difference as a majority of passengers are elites. It is not uncommon for me (PM) to be 20+ on the upgrade list in the mornings. In fact, if you see a GM or FO tag in FC, it is because they had to buy a F/P ticket to get there.

DL is the largest carrier (this was a NWA stronghold, which I was told had the most number of elites per capita than anywhere in the country) and could use their weight to push the airport around a little more. DL is losing customers, as I know of at least 25 elite members that are now flying UA just so they don't have to deal with the security waits. I am sure this number will increase. As I have already re-qualified for PM, I am thinking seriously about doing the same.

<edit> I just checked and CO appears to be on B now. I'll report back after my next trip.