Well, I have discovered that this is not the best approach. The polygon buffers draw the gradients at a specified angle, rather than drawing the gradients in respect to the to and from's (duh). There probably is no practical approach. However, this will help highlight any areas that could be wrong, which helps a little bit. Oh well.
I was going to ask how you dealt with the angle issue for the gradients...
Just brainstorming - I am a big fan of using colour to QA/QC data:
If your 1_2 lines a digitized/stored directionly (to-from) then you could repurpose a script to divide the lines into equal sections
You could then generate sections at say 1, 1.25, 1.5, 1.75, 2.0.
You could then assign colour gradients to the sections
1_1 1.0 is Red
2_2 2.0 is Orange
1_2 1.25 is Slightly less Red
1_2 1.5 is half way between red and orange
1_2 1.75 is almost orange
2_2 is Orange
2_1 1.75 is almost orange
2_1 1.5 is half way between red and orange
2_1 1.25 is Slightly less Red
If I had some free time I'd do a mock-up but in my mind this could work.
Has anybody found a way to achieve this without the need of splitting the lines? It is weird ArcGIS doesn't provide gradient symbology for lines considering other non GIS specialized software do (e.g. R).
I need the From-To direction to be maintained.