I thought to start the mainline first in code 83. Then, do the sidings whenever the code 70 track (weathered) and turnous are available. To complete the mainline, I have a turnout that leads from the mainline into the yard. Code of track to use? The yard itself and the turnouts there will be in code 70.
TIA!
Lee
If your mainline is code 83, then my opinion would be that the turnout off the main should also be code 83. If you plop a code 70 into that spot, you will have to deal with two transitions from code 70 to code 83. If you use code 83, then there is only one transition from 83 to 70.
All of the mainline track should be the same size (code 83 in this case). The railroad would use the heavier rail where the heavy use occurs, and certainly the yard lead would receive that heavy use. This is also better for your operational reliability.
I have seen a number of yards with different sizes of rail within the same yard. You might consider having the "primary" or heavily-used yard tracks in 83 and then drop to Code 70 for the tracks that are on the periphery or are more used for "storage" than for daily use by the railroad.
[yes, there are prototypes for everything, and I recognize that different sizes of rail may be used on the main line of the same railroad due to replacement cycles or areas prone to wear, but for most circumstances, the railroad would always try to put the heavier rail where the most use occurs to reduce their maintenance.]
Bill