Using freight rail when adding passenger service

I've noted that a lot of new passenger service is done using freight rail rather than laying new rail? Is this true? [When] will a point be reached that all rail is too congested?

In some places I think it already has occurred or is near the breaking point. It's just so expensive to lay new rail, and in cities there are concerns about where do you get the land?

I think we can do alot to alay this issue by improving track conditions and signaling to allow faster speeds.

In Portland, much of the rail-based mass passenger transit infrastructure takes place on long-time railroad ROWs, in freeway right-of-ways, or in the middle of underutilized streets.

For example, eastside MAX was built alongside I-84, down Burnside Street, and used the former Portland Traction Company line from Ruby Junction to Gresham. Westside MAX was built using the old Oregon Electric right-of-way from Beaverton Central west to Hillsboro - BN was able to abandon the line and obtain trackage rights on the nearby SP line - there were no freight shippers on the line, and the stretch of the line from Orenco to Hillsboro was already abandoned.

Given that real estate is expensive in Portland (just as with most metropolitan areas) and difficult to cobble up a right-of-way involving hundreds if not thousands of landowners, using a railroad right-of-way suits the bill - only one landowner to deal with, and involves very little demolition of existing structures.

Assembling a new ROW is a pain in the neck. Getting one which is any good is even harder. That's why pretty much every route takes an existing railroad ROW these days.

When possible, abandoned-but-intact ROWs or disused track is preferred. Being in a freight corridor on a separate track is second-best, followed by being in a freight corridor sharing track.

There seem to be enough such routes that we won't be seeing much construction of brand-new ROW for quite a while. Exceptions include downtown access routes, usually.