The New System of the Seattle Subway refers to the lines created after the completion of the initial Bogue System by 1960 and the reorganization of the lines in 1964. In total, this includes Lines 7-13 of the Subway, primarily focused on extending rapid, six-minute-headway lines out into Seattle's suburbs, as well as proposed or under-construction future lines. As Lines 9, 10, 11, 12 and 13 were all opened (or intended to be opened) in conjunction with the 2000 Winter Olympics, New System lines are also often referred to as "Olympic System" lines or, due to their association with Mayor Norm Rice, "Rice Trains" or "the Norm System."
Line 7 - Madrona to Des Moines
The strain on the Dearborn Trunk, 3rd Avenue Tunnel and 27th Avenue Tunnel meant that any additional lines would need to enjoy their own infrastructure, and in the wake of congestion during the 1958 Winter Olympics the Subway decided to extend service into previously-underserved South Seattle, particularly in the proximity of King County Airport, today known as Boeing Field, which at the time was still a small commercial airport that had been frequently used during the Olympics. The Line was placed in its own tunnel bisecting Capitol Hill east-west, beginning at a terminus in Madrona and running through what was known as the Pine Street Tunnel, with connections to the lines on the 27th Avenue Tunnel as well as the Capitol Hill Circulator (Line 6) at stations at 19th Avenue and at Broadway. From there, it continued into downtown, connecting to the 3rd Avenue Tunnel at a new deep station at 3rd and Pike, before entering a tunnel running the length of Western Avenue near the waterfront and then under 1st the entire length of the Industrial District to the Duwamish River, where it emerged onto a high bridge over the river into the South Park neighborhood. This initial line, completed for revenue service in December of 1968, connected people to industrial harbor jobs and was in relatively close proximity to King County Airfield.
More changes were to come, though, as the line was well short of Seattle-Henry Jackson International Airport, then known as Seattle-Tacoma International. Arguments for a route of extension to SEA dominated regional planning discussions for nearly two decades as other lines were opened or streamlined and planned, with a particular debate around the long-term needs at SEA and the placement of its parking facilities. A route and approach were finally decided upon in 1981 and the extension to Seattle-Jackson was finally completed in March 1988, unfortunately a mere eight months before the collapse in air travel during the late 1980s oil crisis began, leaving the line used more sparingly than intended for the first several years of its use. Further extensions of the Line 7 were largely discounted for years, with focus instead placed on running other lines on its infrastructure to get more trains-per-hour to Seattle-Jackson, but a proposal to extend the line to a terminus at Highline College in Des Moines was finally approved by regional planners in 2012 during discussions on how to get more lines extended into South King County, and the Des Moines Extension, despite cost overruns and delays, finally opened in July 2020.
Line 8 - Eastlake to South Center
The Roanoke Tunnel was an idea bandied about in the original Bogue Plan that was put off for years due to concerns about its viability - Eastlake was, after all, already on a major north-south line. However, with spare capacity in the 27th Avenue Tunnel for the time being and a relative lack of interest in ending a future Line 8 at the increasingly obsolete Madison Terminal, Eastlake, via a tunnel under Roanoke, became the most obvious terminus for a new line, and Line 8's opening in 1974 made the neighborhood sandwiched between Lake Union and Capitol Hill thus a major transit hub that it remains to this day. The core of Line 8 was not its small hook west to Eastlake off of the 27th Avenue Tunnel, however, but rather the "New Dearborn Trunk" built between 1971-73 immediately south of the existing tunnel, with stations on the Old Trunk and New Trunk capable of cross-mezzanine transfers between lines using each track. The New Trunk thus opened up considerably more east-west capacity at the south end of downtown Seattle but also was unable to interline directly with the 3rd Avenue Tunnel, and so a new solution was born - running trains out of the New Trunk south, on an elevated guideway over 8th Avenue through the Industrial District. This 8th Avenue Elevated would be designed even in the 1970s to support an interchange station on the Spokane Street Viaduct, and continued on south initially with stops in Georgetown and at King County Airport (allowing airport employees a potential one seat ride to work) and then a final stop at North Marginal until an extension via the Duwamish Bridge to North Tukwila was completed in 1980.
Much like the Des Moines Extension, this remained Line 8's terminus for over thirty years, until a six-kilometer extension to the old South Center Mall campus was completed in 2014 after being approved in 2008; not coincidentally, in 2014, a master plan for a massive eco-district in central Tukwila at the previously auto-oriented South Center site was approved and began construction three years later, and the South Center Extension passed relatively close to the Tukwila station on the Amrail mainline for commuter and intercity rail services.
Line 9 - Eastlake to Burien
Other than small line extensions, the 1980s were a generally quiet time for the Subway, but planning for the 2000 Winter Olympic bid that would succeed in 1993 required a major push for hotel, airport and transport capacity in the Puget Sound region and Line 9 was designed to be a part of that. One major complaint in prior years had been the lack of connection for West Seattle to the rest of the system, which Seattle Mayor Norm Rice declared in 1988 during his inaugural "would be corrected at last" - indeed, planning for a "SkyBridge" over the Duwamish River had begun even before he came to office, but the largest expansion of the Subway since the 1930s/early 1940s heyday was set aside for the 1990s as Seattle boomed and the Olympics loomed. The first piece would be the opening of the SkyBridge between the Spokane Street Viaduct interconnection with the 8th Avenue Elevated, and when Line 9 opened in February of 1992 it ran only to a station at Delridge North, but still West Seattle finally had its subway connection. Phased openings then followed, frustrating residents and transit planners alike as overruns and delays plagued Rice's ambitious "Millennium Project" in the city proper. The line was opened along Delridge Avenue all the way to Delridge South in June of 1994, and finally the Burien extension was wrapped up in August of 1996, a full four years after it had been intended to be complete, though the litigious and expensive story of Line 9 was nothing compared to some of the other "Olympic System" plans that would become infamous over the same years...