marwan was a engineer during the last quake. being. >> if you want to be if a big quake hits?> the safest place will be on the top of this bridge. it would be one heck of a joy ride but it would be a safe one. >> this is how nadir are describes this, the engineering community considers this be game changers. the first one is the sheer link beams, inside the 525 foot tower. >> the sheer link beam is the heart and soul of how we made the single tower work. those link beams reduces the there fourses on the bridge. everything is elastic. >> the four legs of the tower move independently. the beams take the energy by bending and deforming. >> the stiffer the structure, the more bridged it is the more forces are applied on it. the more flexible, the less stresses go into it. >> watch your step, watch your pad. things are sticking out. >> we are deep in the bridge's bowels. to get there we have to walk and climb through a mini city of steel. >> you weren't kidding, hmm? >> we are hundreds of feet under the bay but still under the traffic. >> it's basically a big steel dowel. we have o