Ok, I'm going to try my best here to explain.
I don't have access to the New Interim Worksheet, but it works the same way, just more data placements. (Like Load Time, Stop Signs, Ect.. Cells) This worksheet is Pre RRECS but still works in the same manor.
First here is the worksheet of say RT. 1 and it came out at a 48k. Time to cut it down to a 43k.
If you notice if I change one little thing the whole route eval changes. So I change the use of Gov Vehicle.

It takes away that value and it now drops to a 47K. These numbers have to be correct or you will end up with a wrong calculation of the route. (Only the yellow boxes can be changed, the white show cells show the calculation.) (Remember there is even more cells Like Load Time, Stop Signs, Ect.. with the new one)
After all that is inputted you can now see how many boxes you need to take away to take it down to a 43k.
After subtracting the numbers of central boxes, I need to take away 83 central boxes. (CBU)
I now need to go to the route and find a neighborhood that has close to 83 boxes to take away. Just to start. I find a neighborhood that has 70 boxes. Great, maybe it will work.
Oh, it came back as a 44k. Well that won't work!
But wait, I need to adjust mileage, parcel lockers, dismount distance, ect.
