The last of 1,152 precast road panels for the lower deck of Seattle’s SR 99 tunnel was set into place on March 27, completing the 1.7-mile tube’s double-decked roadways. Along with topping the 32-ft wide slabs with a 2-in. concrete overlay, design-build contractor Seattle Tunnel Partners is currently installing high-tech ventilation, fire safety and traffic management systems, including more than 300 cameras and electronic message signs. Nearly three years late due in large part to numerous difficulties during the tunneling phase, the $2.7-billion project could be open to traffic as early as this fall. That will clear the way for next year’s scheduled demolition of the 1950s-era Alaskan Way Viaduct, which was damaged during an earthquake in 2001.