Franklin said:
Nonsense. It's expensive, but saying it's impossible to put barriers at the Alpe d'Huez is hyperbole. That's quite a broad road with plenty of room.
In the end that's only the only solution: Barriers.
When I said impossible, I was not referring to the fact it is not physically impossible. You are taking my post too literally, and not sufficiently figuratively (as opposed to hyperbolically)
However it would be highly impractical. Does that phrase give you better comfort? We are talking about 20 kms of barriers. Barriers on both sides is 40 kms. Each are about 10 feet in length. The cost is prohibitive. There are not enough gendarmes or volunteers to police them. There are barely enough gendarmes to police the barriers for the last 3 or 4 kms at Alpe d'Huiz.
Erecting the barriers would be an enormous task. Since there are small gaps between the ends of each barrier the custom of people dressing up and running along side of riders would not IMO be deterred by barriers especially on the lower slopes at Alpe d'Huez. They are deterred at the top by the greater presence of gendarmes which tends to inhibit fans from running onto the road. But again the amount of person-power is not available.
The time commitment to put the barriers in place and take them down would be ginormous. I have organized tons of running and triathlon races and I know the headaches of just getting a few volunteers. When the riders come by, in my experience, the fans go nuts, are often drunk and press into the barriers with arms outreached etc. and there is the danger of them coming down onto a rider.
If you think you can convince the organizers, go for it, because the problem is getting worse, but IMO, practicality has its limits on this issue .