What if too many people show up?

OK, I'm not really an organizer for this ride -- but I go to most of them and usually ride sweep, so I'm "associated."

Actually, nobody "organizes" this ride. We send out emails near the full moon and we all just get together in the parking lot and ride out to the town 10 miles away where there's a drive-through ice cream shop.

We've had as many as 100 and I'm hearing from enough people saying "Yes, three of my friends are going to try it!" so this Friday's might be just. plain. huge.

What can we do to keep this from being a major hassle & hazard?

I'm thinking: break up the start ... find some somewhat arbitrary way to break things into groups... definitely "paceline people go first!" -- maybe just arbitrarily divide things up... or as people start heading out, just stop them every once in a while as if it were a traffic light and pretend to wait for an imaginary green?

Seems to me that in order to organize/break up the start, you would need someone to step up and be the "organizer."

If everyone is riding the same route, then breaking up by average speed categories probably makes the most sense. But you'd want to make that plan clear in the emails because trying to tell a large group of people about it at the start will be difficult.

You had me at a full moon ride and ice cream :)
I agree with N.Y. on the initial email. Having info about safety and it being the major concern in that email would help too. That should be a ‘copy and paste’ case in any size group ride email though. Assuming the ride is on Friday night’s full moon you could still get an email reply to participants out about safety and yes, the possible large number of riders and a staggered start if necessary. For 100+ riders having three groups, fast, medium and leisurely could help. Managing a crowd of cyclists eager to ride can be a daunting challenge though. I’d look at it as a learning experience if things don’t work smoothly this time knowing it will get easier in the future with consistency.

Thanks! Yup, we'll have an email and a "chat before the ride" about not crashing. And how if you want to go slowly enough you can ride with me :)

DH and I do 2 bigger rides a year and both are show and go. Otherwise, the rides we lead are screened by me for the person's appropriateness for the ride. After doing the larger rides for a couple of years (sometimes there are 40-60 people on these rides) we got at least 2 more leaders involved and split the group in 2 at the start. DH and I lead the faster group (not fast by most club standards), with an average of 14-ish. So, as sweep, I end up with people averaging 13-ish, sometimes we are tighter together. The slower group averages 10-12, but one year, we had a real new rider (she had just learned to ride) who ended up coming in with the sweep at an average of 8. So, DH and I leave first and we tell the leader of the second group to wait 5 minutes and go. It's the same route, so if someone at the back, with me, and is struggling, I just have them pull over and wait for the next group. You could do something like that. Also, the other club I ride with tries to keep no more than 8 people together in a group, leaving a gap between groups. We've had some complaints and the police called on us when we are riding in large groups, mostly because of bad behavior of riders.
When I lead for AMC, we are required to keep our group together and have a sweep to meet liability rules. The rules are based on hiking, but we have adapted. We just tell someone who wants to go ahead they are free to go, but we have no responsibility for their "care," if they do.

Thanks! Since this was a night ride, it was kinda like that, though there was an honestly fast group out the front. We had roughly 75 people -- and we sent "the fasties" out and then there was an appropriate shuffle and three separate groups left, so drivers could actually get around us as we got out onto the prairie.
The only unpleasant part was approaching SIdney when we approached the road to turn let on, and a car was heading our way on it... and my buddy headed off the road to the left. I just stopped waiting for the driver to go by and... s/he just turned my way. I had blue lights all through my spokes so s/he saw me but really had to slow down... and yes, it was an "OH CRAP" moment during which I never know what will come out of my mouth, but it was (in full middle school teacher to the back of the room voice), "If you had signalled I would have gotten out of your way." The driver went on and we went and had ice cream at 48 degrees...
Now to get out and lead the a.m. ride, prob'ly to the same location ;)

I'd definitely break up the start, for sure. But I have to say- many would LOVE to have too many participants!!