More than a year before the new State Route 99 tunnel is scheduled to open to vehicles in Seattle, I took a ride Thursday from one end of the 2-mile tube to the other, beneath this booming city and its waterfront. While the views weren’t as spectacular as those from the aging Alaskan Way Viaduct that the tunnel will replace, the experience felt like an historic journey into the future of transportation in this city.

Starting at the south end near CenturyLink Field, members of the media were loaded into a tram of sorts — a metal-caged vehicle with bench seating used to move workers. The vehicle moved away from the light and views of the sky and into the dimly lit tunnel at a relatively plodding pace, avoiding workers and equipment along the way and sounding the horn regularly to announce its approach.

We traveled along the lowest level of the tunnel in what will eventually be the bottom surface of a maintenance pathway — a space beneath the lower roadway surface of the double-decker highway. It’s situated between the corbels, or ledges, that will support that lower deck.

Much of the tunnel has progressed beyond the circular shape created by Bertha the boring machine and the concrete rings laid in her path to create the tunnel’s outer wall. Interior walls have been poured, and most of the upper southbound roadway has also been installed thanks to a “cast in place” method — visible in this time-lapse video from the Washington State Department of Transportation.

So cruising through the tunnel on Thursday felt like driving through a rectangle — with lots of Honey Buckets and tools along the way.

The 10- to 15-minute ride (at just a few mph) ended near the north portal close to Seattle Center and the Space Needle. This is where Bertha finished her years-long push beneath Seattle and popped back into daylight on April 4. Seattle Tunnel Partners spent the summer cutting the tunnel boring machine and her 5-story-tall cutterhead into pieces, lifting them out of the receiving pit and trucking them away. That process concluded at the end of August.

The progress that’s been made on building the upper roadway was starkly evident here, as well. Several hundred yards from the north end of the tunnel, the roadway stopped, with rebar protruding high above, waiting for the concrete to catch up to it. At more than 90-percent completion, 159 of 171 concrete pours have been made on the upper deck.

Walking up an incline away from the tunnel and back toward daylight on what will be the northbound roadway, a sign has been installed to alert future drivers of the toll they’ll be paying for the fancy highway they just used. It’s the same as those mounted on the SR 520 bridge over Lake Washington. The road also splits here, with the option to continue north on 99 or exit at Dexter Avenue.

After gawking for a while at the opening where Bertha made such a dusty appearance last spring, we hopped back in the tram for a return trip to the southern end.

It felt good to see the sunlight again and fill the lungs with fresh air. A Seattle Sounders FC flag was visible, flapping in the wind on a building overlooking the stadium where the team would be playing Thursday night.

The Seattle skyline was also visible, but for those who have always appreciated that view — and the water, ferries, mountains and sunsets to the west — as they drive north along the upper deck of the Viaduct, the uniquely Seattle scene will fall out of sight as you drive down into the tunnel.

But it was a big day at this end because precast panels for the tunnel’s lower deck roadway began showing up this week from Tacoma, where they are being made by Concrete Technology Corp. They’ve been building the panels — which are 32-feet wide and 8-feet long and weigh 22 tons each — since the beginning of the year, and the lower deck will take 1,152 of them.

A specialized crane (called a precast gantry crane), built to slide along temporary rails inside the tunnel, will lift and place the slabs on top of the corbels on both sides of the tunnel. Once they’re fastened in place, a layer of concrete will be laid over the top to create a smooth driving surface — unlike the bumpy ride I took on the way in and out.

Work continues on the mechanical, electrical, and plumbing systems inside the tunnel, and is expected to be completed by next March. The lower deck installation should wrap up by the end of 2018, as the entire project shoots for a January 2019 opening — which will bring with it the start of the Viaduct’s demolition.

As project administrator Joe Hedges of WSDOT said on Thursday, more than four years after Bertha first started cutting a pathway beneath Seattle: “There is light at the end of the tunnel.”