The viaduct was tall, had concrete railings, and was supported by 400 columns spaced approximately every . SR 99 formerly transitioned from a surface freeway to the double-decker elevated viaduct near South Holgate Street in SoDo, approximately north of the First Avenue South Bridge and beyond an interchange with the West Seattle Freeway near Harbor Island. The freeway then ran between the Port of Seattle's Terminal 46 and the Seattle Coast Guard Station to the west and the BNSF Railway container yard to the east. It passed a set of ghost ramps near Safeco Field that were originally planned to accommodate a freeway connection to Interstate 90 that was never built. Near CenturyLink Field, SR 99 reached the terminus of the original (and post-2011) viaduct and the south portal of the future downtown bored tunnel, using a set of diagonal ramps parallel to Railroad Way to reach the central section of the viaduct. The viaduct expanded from four lanes to six lanes and turned northwest as it followed Alaskan Way and the city's waterfront on the west side of Pioneer Square; the area underneath the viaduct was used for street parking between construction periods. It passed east of the state ferry terminal at Colman Dock and reached a set of ramps serving downtown traffic: the Columbia Street onramp to the southbound lanes and the Seneca Street offramp from the northbound lanes. The waterfront section of the viaduct was noted for its scenic views, which include Elliott Bay, the distant Olympic Mountains, and the city's skyline. Between the Seattle Aquarium and Pike Place Market, the double-decker viaduct ended as SR 99 split into a pair of side-by-side elevated lanes that traveled over the north portal of the Great Northern railroad tunnel and under Victor Steinbrueck Park. SR 99 then came to an interchange with Elliott and Western avenues, which marked the north end of the viaduct and the south end of the four-lane Battery Street Tunnel. The Western Avenue crossing included a notch in the southbound railing of the viaduct, which was cut out to pass around a column of the Seattle Empire Laundry Building. The Alaskan Way Viaduct was one of two north–south freeways traversing Downtown Seattle, the other being Interstate 5 to the east. Traffic volumes on the viaduct, measured by WSDOT in terms of average annual daily traffic in 2015, averaged approximately 91,000 vehicles south of Columbia Street