I believe there were several groups involved, or at least elements of several groups, but only two had billboards:

A new modular layout to me was the Colorado Rail Link, an HO scale layout that seemed to be BNSF oriented, with a focus on modern operations -

Welp, my old house is finally on the market and I can take a moment or two to relax and collect myself before I roll up my sleeves and get to work prepping my new layout room. It's taken longer than anticipated to get to this point, but I'm glad I am here now!

In the meantime, I also submitted a picture to the Ripley's Unconventional Art Contest.

This is a club that I've seen twice that I know of - because they won awards in Anaheim in 2008 and Orlando 2017:

Having built several resin car kits now, and wanting a challenge, I have started a Speedwitch Media A. E. Staley Tank Car kit. 

Being rather fond of organization, I started assembling Project Logs for my locomotives.

Nick Brodar

Frankly, when I looked at these photos I realized that I had no idea who's layout this was. But I see that the T-Trak page on Facebook is noting that they had an HO layout there as well and a namebadge of someone sitting at the layout that I caught in the corner of a photo indeed said T-Trak on it.

So here it is:

By now I expect that many people in the hobby have heard of the record setting T-Trak layout at Kansas City. According to the layout's Facebook account, there were 340 modules of varied sizes, the equivalent of 732 single T-Trak modules. The mainline run was 28.4 scale miles.