How do you stop a big truck from driving into a small tunnel?

Answer: a water curtain stop sign

by Colin Wood / February 28, 2014

In Sydney, Australia, vehicles that are too large to fit through the tunnels they approach are met with a curtain of water, upon which a stop sign is projected. The sign is hard to miss because it takes up the whole entrance to the tunnel, but if the truck fails to stop in time, no sweat, it’s only water.