These bridges are in the wilds of the outback. They might see five KIDDIES a year...
The objective of the protestors is clear. They wish to minimize nearby freeway traffic elsewhere ~ one way is to make sure conditions at that tunnel are miserable.
I saw they had a fire there once. I couldn't help but observe that this "wilderness area" had a brushfire in the early 1990s that swept down and destroyed over 3,000 homes nearby.
Are you from Los Angeles perhaps?