Seattle’s new SR 99 tunnel has a stacked roadway inside. Crews recently finished pouring the upper southbound roadway. Now the lower northbound road is under construction as shown in this time-lapse footage. Unlike the top deck, the lower surface is built with concrete panels constructed off-site, each one weighing 22 tons. The pre-made panels are trucked into the tunnel, lifted with a specialized crane and joined together to create a functioning highway. The tunnel was created by the huge drilling machine Bertha as part of the $3.2 billion Alaska Way Viaduct Replacement Program that is scheduled to be complete in 2023. Video courtesy of WSDOT.