I have been on a few organized rides and organized one myself. These were from 15 to 800 riders. If they are not large fund raising events you will not get police road blocks. I planed a 45mi, 15 rider rural rout with few high traffic intersections. Ride the rout just before the event to make sure all is clear. Print a map to hand out with a couple of cell phone numbers just in case. Get at least 3 other riders involved in the planning, you need extra leaders and end riders. It is illegal to block intersections, and dangerous as well. On a long ride plan lots of stops so riders can regroup if necessary. At some dangerous intersections you can have a rider go ahead and position themselves safetly off the road to wave riders through. You need to have everyone present for a safety briefing, take charge, be loud, because everyones safety is serious business. If you have not been on an organized ride, you better go and experience one or two.