The ADA access near the intersection of Front and Walnut is apparently now complete. This access point is part of the recent Route 441 bypass project. Previously, this ADA terminated at the rear egress. In other words, it didn't go anywhere.
Now, however, asphalt has been applied, as shown above, creating a wheelchair accessible walkway running parallel to the railroad tracks, allowing entrance to Columbia River Park.
Here's a view from across the street at the Eastern Drillers building (the old railroad station).