tl;dr: "Too long; didn't read" - often applied to "wall of words" posts in forums. I'll keep this a short, sweet primer!
Eclipse Planners: Three Things to Make or Break You
This is the big headache - as people stream into your community, you'll find roads busier than normal, and those intersections that are a pain on a normal day (you know the ones, you take a 3 min detour to avoid them during busy times) will become a NIGHTMARE leading up to and immediately after the Eclipse.
Traffic planners, the Road Departments, and Law Enforcement for localities all need to sit down and come up with a solid, viable plan to move people around, especially those who are unfamiliar with the area! You'll want to consider:
One-way roads in congested areas to ensure smooth traffic flow
Temporary stoplights for busy 4-way intersections
Readerboards to direct people to desired locations
Temporary road closures to protect infrastructure or sensitive areas or allow "bypasses" for public safety/public works to get around heavy traffic to respond to issues
How do we avoid the "mass exodus"? Can't we get them to stay another day?
Realistically? You probably can't, not enough to make a significant difference anyway. Like 2017, this eclipse will be on a Monday during the school year. People might take the day to be there, plus a day or two for return travel, but the reality is they will have to get back to work and/or school. Make efforts to retain people, sure, but don't expect they're going to "slowly filter out". My experience in 2017, from Dixie Pass at 5,000ft on Highway 26 in Eastern Oregon - the Centerline of Totality - as soon as Totality was over, car doors were slamming and people were flooding the highway. Hours of backup and L.A.-style traffic jam ensued all over the area on Highways 26 and 395. I welcome folks to try to stop that from happening, but I'm not optimistic about your chances.
Toilets & Sanitation
25+ years in public safety with the attendant dark humor leads me toward making an obligatory "crappy day" joke. Let's stipulate it as made and move on - because this really is NO JOKE.
Having spent 14 years with the US Forest Service in Fire/Emergency Management, I've been part of numerous "Fire Camps" where hundreds to thousands of firefighters and support personnel eat, sleep, and receive equipment, supplies, and briefings, usually staying for 14-21 days at a time. "Camp Crud" is a serious issue even in clean well-maintained camps, and you don't want your Eclipse-goers and event attendees remembering your town as "that place we all got sick for the Eclipse".
Carefully consider your needs, not just for porta-potties but handwashing stations as well. Washing your hands is vitally important to preventing "the crud" or more serious disease transmission, so make handwashing stations a "must" along with your porta-potty order.
There are numerous websites that give you formulas or a calculator for how many porta potties you'll need, they're easily searched by something like "how many porta potties for an event".
Tying back to Transportation - if you're using those porta-potties for more than a couple days, say at a campground to expand your capacity, or a private landowner renting camping space in pastures or fields, those potties will need to be serviced as well. Likely every sanitation company even remotely close to Totality will have every potty & handwash station rented out - that also means their service staff will be busy so count on extended times for them to get around to service you, especially given the increased traffic flow prior to the Eclipse!
Tag and extend on the "sanitation" theme - not only is trash everywhere an ugly and unappealing look and feel for your event or community, it's unhealthy.
Arrange ahead of time to stage dumpsters at strategic locations and have them emptied - again remembering that transportation theme: it may take longer for garbage trucks to make a run to the landfill and back, so plan for extra capacity!
Campgrounds (whether established or "ad hoc" like the farmer renting camping space on his land) and parks are going to need that extra capacity. One thing we found on the Malheur NF during our 2017 Totality experience was that people were seeing trash bins at campgrounds or picnic areas they weren't staying in, but they would stop in and do a "drive by" drop of their trash on the way out.
Two ways help prevent this:
Messaging beforehand: variations of the "pack it in, pack it out" messaging and nature ethos that backpackers and wilderness enthusiasts are already familiar with
Outside the box thinking: establish "trash collection points" where you can use stakeside trucks to transport trash to the landfill as well - this tactic worked for us on the Malheur in 2017 when all the extra dumpsters in the area were already rented out
The Big Take-Away
If you're just now starting to think about these things, you are behind the power curve BUT! you're taking the right steps even if they're a little late. You may also be behind the "rental curve" and struggle to find vendors even remotely nearby who aren't already booked solid and can meet your need for traffic control devices, porta-potties, handwash stations, and dumpsters - along with the people and equipment to service them for the week before and after. Time to come up with some "creative problem-solving" and "outside the box" solutions.
Oh yeah, there's the cleanup piece too - Monday afternoon/evening everybody will be POURING out of your community, by Monday night the place will look like a ghost town compared to the week prior and especially the weekend before. Empty food bags and wrappers and discarded eclipse glasses will blow through the streets, and then begins the "recovery" process - you're going to need people along with those extra dumpsters, pickups, and stakeside trucks to mount the cleanup operation, even if you "did everything right". Wrap-up and cleanup will take a couple days even with a dedicated crew, so you'll want to keep the dumpsters around and serviced at least a couple days post-event.
Are you flapping off the back end of the "rental curve" and need porta-potties, handwash stations, traffic control devices, and dumpsters plus service for them?
Sorry, Grounded Truths CAN'T help with that - I wish I could because I would be rolling in dough if I had that kind of capacity. What I can help with is planning to help mitigate those impacts and some creative problem-solving and those outside the box solutions to help you be successful this fall and next spring with the Annular and Total Eclipses!