Bridges breach a barrier by the addition of something new, whether wood, steel, or concrete. In contrast, tunnels breach a barrier by the subtraction of something already there, whether rock or earth. Bridges display the technological genius of human beings. Tunnels display their brute force, in this case rock dynamited into rubble and hauled away by vehicles built of iron and powered by fossil fuels. The post in the distance carries metal wire, which carries electrons, which carries human communications. This is a bridging technology as well.