Take a look inside the tunnel that will replace the Alaskan Way viaduct

The downtown Seattle tunnel that will replace the Alaskan Way viaduct is edging closer to completion.

The upper level of the double-decker highway is about 90 percent complete, according to project manager Chris Dixon.

Crews are now getting ready to start building the lower roadway inside the tunnel.

More than 1,100 concrete panels will be used to build the lower roadway. Each one weighs about 44,000 pounds, or roughly the same as two and a half T-Rex dinosaurs.

According to Dixon, the project is on target.

"Our schedule right now is to achieve substantial completion by October of next year, which leads to opening the tunnel to traffic in early 2019," he said.

Speaking to media after a guided tour of the two-mile underground project, Dixon said it's been smooth sailing since the tunnel was completed earlier this year.

However, there are still unknowns related to the project. A dispute over who will pay for massive delays and cost overruns that occurred during tunneling is ongoing. Toll rates for the tunnel have also yet to be set.

When the project is complete, cars traveling on state Route 99 will move underground for a two mile stretch under the city.

The process of removing the aging viaduct will start when the tunnel opens.