Did we meet?
Like you said, this originally wasn't our responsibility (we were responsible for the roads across/around the market area), but after this incident some of our team were moved to the railroad as well.
It is inevitable that vehicles have to go down roads where festival goers are walking and from a traffic supervisor point of view, both people driving vehicles and the punters could do a better job preventing these accidents. I've seen cars driving around like they own the road, shouting at me that I wasn't getting them trough a vast crowd fast enough. On the other hand, punters that cross the road right in front of cars and ignore signals that should help prevent these accidents from happening can expect little of my respect. In the end it all comes down to patience and giving each other space to move.
99% of the times there are no problems though. Like @ohmygod said, when it gets to crowded (part of) the route gets locked down and I think the one way system in the market area works great.