There are few area public works projects as video-heavy as the upcoming, long-delayed State Route 99 tunnel project. Last month, we saw a side view of the northbound roadway coming together. But yet another time-lapse video, embedded above, gives a better sense of how the tunnel’s layers stack on top of one another.

Because one end of the tunnel is slowly being built into a 90-foot-deep pit where Bertha the tunnel-boring machine emerged last April, this segment of the tunnel has kind of a window into the roadway.

Over the course of a minute and a half, the video shows crews pulling the lower, northbound roadway together before pouring in the upper, southbound roadway. Because this segment is outside the bored portion of the tunnel—this part is cut-and-cover—it shows almost a cross-section of what the final project will look like, including walls and ventilation systems.

Crews just finished the lid for this section of the tunnel last week.

The 1.7-mile-long roadway is more than half finished, with the entire southbound roadway complete—not including some walls on the west side—and the northbound roadway two-thirds of the way there.

Bertha the tunnel-boring machine officially finished the length of the two-mile tunnel, which will take cars past downtown along SR 99, on April 4 of last year. That was a few years behind the original schedule, which estimated the tunnel would open in December 2015.

The new roadway is set to open in early 2019. After it opens, the aging Alaskan Way Viaduct will come down.