Once they're out of the chicane they're not going to be hitting Arenberg in a big group, it's basically going to be single file starting from a relatively very. slow speed.
theyll be in a huge massed group of riders as theyll all have come to a complete stop to negotiate the new turn, wiping out any advantage anyone had gained and will then try to sprint as fast as they can away to be first onto the cobbles, because then you get to pick your line and arent worrying about the line of the rider whose tyre tracks you are left following or if the guy next to you is going to go down.
have you not seen how a cyclocross mass start works when they hit the first acute turn corner ? all the ones at the front make it out without crashing all the ones stuck in the middle hit the deck as one rider makes a mistake falls, or unclips the bike flips sideways and becomes a barrier and everyone piles into them.
you know a bit like the Koppenberg last week.
if you want to make Arenberg safer, and we can debate till the goats come home about whether thats actually something we want, but its not about speed, its about the mass of riders on sections at a time all fighting for space, the crashes happen among groups or clusters of riders.
so stretch the groups out, by making the race harder before Arenberg, limit the start numbers, over 200 riders across 25 teams is a stupid number to contest a race like this
I actually think the simplest way to do it is to funnel the riders on to Arenberg, using a bottleneck and narrowing the width of the road to force them into riding a narrower line , just like on the cobbled climbs, and borrow some airfences from MotoGp not stupid metal fences with legs that stick out and lots of things handlebars and pedals can get stuck in to do it.