From what I have learned about the East Portland Connector, the issue is about improved freight rail traffic flow through east Portland.

Union Pacific's mainline from the Columbia Gorge splits at Troutdale, Oregon 1) the Kenton Line and 2) the Graham Line. The Kenton Line allows traffic to move through north Portland to Peninsula Jct. where traffic can head north to Vancouver, WA, west to the Barnes Yard, or south to Albina Yard. South of Albina Yard, traffic winds slowly through inner Portland to East Portland Jct where trains can head west across the Steel Bridge to Union Station/Lake Yard interchange or diverge onto the western end of the Graham Line or continue south to Brooklyn Yard/Willamette Valley. The Graham Line follows along side of I-84 through east Portland and connects to the Kenton Line at Troutdale.

From East Portland Jct. south, this had historically been Southern Pacific territory and the Graham line was configured to allow UP to head north to Albina or west to Union Station. In later years the track arrangement only allowed through movement to and from Albina Yard

I don't know the origninal history of the Graham Line but I lived along it during the 1970's and 80's. There were a few rail served industries between about 33rd and 181st and I remember the Amtrak Pioneer utilized this line.

Since UP merged with SP, there has been interest to establish a connection which would be the south leg of a wye that would allow through traffic between Brooklyn Yard and Hinkle Yard to bypass Albina Yard, thus improving the overall traffic flow through this portion of Portland.