What material would be best to build a bridge lowering arm?

[DonRotolo]

Certainly a solid. Gases, liquids and plasmas would cause problems.

Cast iron? Seriously? Aside from it being far too heavy, it is not very tough: It breaks easily.

Most teams will be using aluminum. Some will use wood, or perhaps Lexan. None will use Plexiglas (Acrylic) because it is dangerous.

[ksafin]

I'd say an aluminum tube. Our bridge lowering design is simply an aluminum tube connected at each end to two arms that lower and raise the tube.