Vehicle plows into crowd on Bourbon St., with 14 fatalities

As for maintenance on the retractable bollards...the problem is things getting stuck down in the gap, like Mardi Gras beads and various other things, am I correct? If that is a problem, why can't they just add a cap to them with a flange that fans out a few inches? Basically just a protection measure, and it would add a slight bump, like a speed strip when retracted. I've seen this in other places.