Portland city planners originally conceived the idea of a northside passenger rail service in 1988 as part of Portland's Central City and Albina Community plans.
These plans sought to extend the region's then two-year-old light rail system called MAX (for Metropolitan Area Express) through North Portland across the Columbia River and into Vancouver and Clark County in Washington via potential routes on either North Interstate Avenue, Interstate 5 (I-5), or Northeast Martin Luther King Jr. Boulevard (formerly Northeast Union Avenue).
As members of the U.S. Senate Committee on Appropriations, Oregon Senator Mark Hatfield and Washington Senator Brock Adams combined these proposals with a greater Portland–Oregon City light rail plan endorsed by Metro regional government, for which the committee appropriated $2 million in 1989.

Preliminary alignment studies to Clark County, including an additional proposal for a line between Vancouver Mall and Clackamas Town Center along I-205, commenced shortly after.
Planners identified a 25-mile (40 km) route from Hazel Dell through downtown Portland to Clackamas Town Center in 1994 they officially named the South/North Line.
63 percent of Portland area voters approved a $475 million bond measure in November to cover Oregon's portion of the project's estimated $2.8 billion cost.
Across the river, Clark County requested a 0.3 percent increase in sales and vehicle excise taxes to provide Washington's $237.5 million share, which voters turned down by 69 percent on February 7, 1995.

Amid fears that ridership would not justify a North Portland segment if Clark County were excluded, TriMet scaled back the project and released a second plan to build the line up to the Rose Quarter.
Though backed by the state government, light rail opponents forced a statewide vote that defeated the proposal in November 1996.
In an effort to regain the support of North Portland residents, who had historically voted in favor of light rail, TriMet announced a third plan in February 1997 that proposed a 15-mile (24 km) line from Lombard Street in North Portland to Clackamas Town Center.
This line would have run along the median of North Interstate Avenue, crossed the Willamette River on the Steel Bridge, run along the Portland Transit Mall, and crossed the river again on a new span farther upstream (south) near Caruthers Street.
The Portland City Council subsequently mapped a longer alignment through North Portland that would have terminated the line another mile north of Lombard Street in Kenton.

In August, due to the wording on the original ballot passed in 1994, which described the line extending into Clark County, the TriMet board elected to reaffirm voter support by drafting a new $475 million bond measure.
Portland area residents cast their vote on November 3, 1998; those against the measure narrowly defeated it, 52 percent to 48 percent.
With the South/North Line effectively canceled, light rail on the Portland Transit Mall and to Clackamas Town Center would not be built until 2009 for the Green Line.
Much of the proposal's southern half from the transit mall to Milwaukie would also remain shelved until the opening of the Orange Line in 2015.
Portland city planners originally conceived the idea of a northside passenger rail service in 1988 as part of Portland's Central City and Albina Community plans. These plans sought to extend the region's then two-year-old light rail system called MAX (for Metropolitan Area Express) through North Portland across the Columbia River and into Vancouver and Clark County in Washington via potential routes on either North Interstate Avenue, Interstate 5 (I-5), or Northeast Martin Luther King Jr. Boulevard (formerly Northeast Union Avenue). As members of the U.S. Senate Committee on Appropriations, Oregon Senator Mark Hatfield and Washington Senator Brock Adams combined these proposals with a greater Portland–Oregon City light rail plan endorsed by Metro regional government, for which the committee appropriated $2 million in 1989.
Preliminary alignment studies to Clark County, including an additional proposal for a line between Vancouver Mall and Clackamas Town Center along I-205, commenced shortly after. Planners identified a 25-mile (40 km) route from Hazel Dell through downtown Portland to Clackamas Town Center in 1994 they officially named the South/North Line. 63 percent of Portland area voters approved a $475 million bond measure in November to cover Oregon's portion of the project's estimated $2.8 billion cost. Across the river, Clark County requested a 0.3 percent increase in sales and vehicle excise taxes to provide Washington's $237.5 million share, which voters turned down by 69 percent on February 7, 1995.
Amid fears that ridership would not justify a North Portland segment if Clark County were excluded, TriMet scaled back the project and released a second plan to build the line up to the Rose Quarter. Though backed by the state government, light rail opponents forced a statewide vote that defeated the proposal in November 1996. In an effort to regain the support of North Portland residents, who had historically voted in favor of light rail, TriMet announced a third plan in February 1997 that proposed a 15-mile (24 km) line from Lombard Street in North Portland to Clackamas Town Center. This line would have run along the median of North Interstate Avenue, crossed the Willamette River on the Steel Bridge, run along the Portland Transit Mall, and crossed the river again on a new span farther upstream (south) near Caruthers Street. The Portland City Council subsequently mapped a longer alignment through North Portland that would have terminated the line another mile north of Lombard Street in Kenton.
In August, due to the wording on the original ballot passed in 1994, which described the line extending into Clark County, the TriMet board elected to reaffirm voter support by drafting a new $475 million bond measure. Portland area residents cast their vote on November 3, 1998; those against the measure narrowly defeated it, 52 percent to 48 percent. With the South/North Line effectively canceled, light rail on the Portland Transit Mall and to Clackamas Town Center would not be built until 2009 for the Green Line. Much of the proposal's southern half from the transit mall to Milwaukie would also remain shelved until the opening of the Orange Line in 2015.
MAX Yellow Line