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Known as the city's most densely populated neighborhood and a destination for many packed bus lines, Chinatown has nonetheless been bypassed by San Francisco's ambitious rail projects throughout the area's 169-year history.

That will finally change with the completion of the long-planned and transformational but often contentious Central Subway. ISFMTA’s first subway extension in decades, the project will begin at Fourth and King and terminate at the new Chinatown Station currently in progress.

When finished, the route will forge a literal connection between two traditionally underserved communities: The southeastern neighborhoods that the city sees as the future of San Francisco, and Chinatown, one of San Francisco’s deepest wells of history and culture.

Here’s everything to know to be in the know about that long and winding road—or, in this case, tunnel:

In 1998 the city calculated a 1.75-mile route from King Street all the way to Jackson, but the commonly cited estimate today pegs the length at 1.7 miles.

There will be one new street-level station at Fourth and Brannan (servicing Caltrain and rerouting the T-Third Street from its present Fourth and King stop) and three new underground stations: Yerba Buena/Moscone Station at Fourth and Folsom, Union Square Station at Stockton and Market, and Chinatown Station at Stockton and Washington.

Tunnel-boring machines dug beyond Chinatown and into North Beach. Despite speculation that this is literal groundwork for future extensions, the San Francisco Chronicle reported that it was just the nearest spot with enough room to extract the machinery.

The San Francisco Board of Supervisors wanted to name Chinatown Station after late Chinatown lobbyist Rose Pak, in recognition of her support for the project and neighborhood, but SFMTA maintains that stations should be named for their locations.

The Central Subway is in phase two of a two-stage plan to expand light rail service into neighborhoods previously never undermined. Phase one was the T-Third Street line that opened in 2007, which will soon connect with the Central Subway to form a single route.

Upon completion, the light rail will extend from Visitacion Valley to Chinatown, but at various points over the years plans looked as far south as Caltrain’s Bayshore Station and as far north as Fisherman’s Wharf.

The subway line broke ground in February 2010, but the planning phase stretches back to the 1990s.

Tunnel boring took place between June 2013 and July 2014. The boring machines weigh roughly 750 tons each and are more than 100 yards from one end to the other.

The pair of titanic tunnelers bore the nicknames “Big Alma,” after San Francisco philanthropist Alma de Bretteville Spreckels, and “Mama Chung,” after Chinatown’s Margaret Chung, the first Chinese-American physician.

The Central Subway tunnels pass beneath BART and existing Muni tunnels at Market Street, with as little as 7 feet between higher and lower passages at some points.

The city demolished the classic but decrepit Pagoda Palace Theater in 2013 to make an extraction point for the tunnelers. Beneath that circa 1909 building, crews discovered the foundations of the church built on that spot in 1888, another victim of the 1906 earthquake.

Originally scheduled for completion the day after Christmas 2018, the Central Subway now lags almost a year behind thanks to scheduling conflicts with contractors, reports the San Francisco Examiner. The new projected finish: December 10, 2019.

On the bright side, delays have not yet put the Central Subway over its $1.57 billion dollar-plus budget.

Tutor Perini, the contractor at work on the delayed station builds, netted the $838 million work order in 2013, the largest contract SFMTA has ever handed out for construction.

The budget breakdown: $44 million-plus for planning and conceptual engineering, $113 million-plus for design engineering, $34 million-plus for securing right of way, and nearly $1.4 billion for actual construction, most of that for station building.

As critics of the project are fond of pointing out, the finances factor out to roughly $176,000 per foot of rail line.

Over $983 million of the funding comes the federal government, with extra $471 million-plus from the state, and nearly $124 million in sales tax revenue from Prop K.

SFMTA predicts that when finished the route will carry “nearly 73,000 passengers a day,” and anticipates that by 2030 it will be the busiest and most frequently used of all the city’s subway lines.

Artist Yumei Hou will create a pair of 30-by-35-foot “laser-cut metal artwork installations” for Chinatown Station depicting Chinese folk dancing and featuring “some of the dance’s most iconic folk heroes such as the Monkey King, the White Snake and the dragon mingled with scenes of country life,” according to the San Francisco Arts Commission.