Generating flow map with varying width and alpha level which accumulates using ArcMap

I’m using ArcMap.

I have a very large line shapefile with ~300’000 links which all have the attribute flow (a numeric variable from 0-200).

My goal is to display a map like in this example (produced in QGIS):

This map is from the following this link. There are more

Basically I want to have a varying (and adjustable) width of the links, according to the value of flow. Ideally, the color of the links should contain an alpha value, to see overlapping links accumulate.

I have not been able to find anything on codeshare that could help me with this issue.