forecast_variable field is redundant if we are just working with volumes

[e-lo]

From tester:

Since we were working on Volumes, I do not feel need to add Forecast_Variable field. This field has options as ridership, boardings, speed, etc.

[e-lo]

Even if we just have volumes (which we don't need to be), we might have special volume types (hov, toll, etc) which would be useful.