Eggy - this will probably bore you and you didn't even ask the question. I'm not a specialist but I have a bizarre fascination for production and logistics.
Number of finishers and their times.
Sub 3 - 1000
3h00 to 3h30 - 5000 (30 mins)
3h30 to 3h45 - 6000
3h45 to 4h00 - 6000
4h00 to 4h15 - 5000
4h15 to 4h30 - 4000
4h30 to 4h45 - 4000
4h45 to 5h00 - 3000
5h00 to 5h30 - 3000 (30 mins)
+ 5h30 - 3000
Eggy you experienced more congestion than previous years because you finished during rush hour, also you were running quickly thus people were in your way. Previous years when struggling then you would have been in their way.
I thought Paris was inefficient due to the long delay at the start. Au contraire ! Having a staggered start even within the same pen means that the finishes period is longer. Imagine 3h30-3h45 pen started at once and everyone was in the correct pen. At the finishing line, everyone would arrive in a 15 minute period 3h30- 3h45 after the start. Due to a 5 minute the delay, the finishing period would be 20 minutes long even though everyone finished under 3h45. Reducing the flow by a third.
I don't think the Seine is a particular narrow area but if you started 5 minutes before or after then your bottle neck would have been 1k earlier or later. You only need a small number of runners in difficulty to block the others.
The people in the wrong pens may be a good thing as it spreads the group out but the faster runners need to choose the correct running line. I don't know if this is experience or luck.
Racing etiquette is not spoken about, perhaps the French run like they drive or shop, hogging the lane leaving their trolley in the way. How could organisers improve the flow ? There are very few big races so it's trail and error, I doubt there is going to be a job for a marathon production planner. Other factors could impact the race, certainly the weather on the day, higher temperatures would increase the number of strugglers and reduce the distance where runners will start to slow.
You could start in a higher pen, fewer people in front, you will become the obstruction instead of being obstructed. I have thought about starting at the back, if I ran 4h pace then I wouldn't catch someone finishing 5h if they started over an hour ahead. The majority of the field would have finished before me, the runners on the course would be fewer but also slower, would this be a problem ? I might contact the organisers to see if there is a nerd.
KeyserSuze - I'm sitting in bed, finding excuses before I got and cut the hedge. I contributed very little last year and I'll probably be AWOL again so it is better if someone else takes the lead. Pleased to see Mr KS is joining the party also it's best to sign up first and find your mojo on the way. I was training badly so I wasn't enjoying it, got advice from the thread and although it was too late for Paris this year I'm feeling miles better. In fact 26.2 miles better.