Consistent sub-categorization of road transportation

[danielhuppmann]

While working on #255 for @jkikstra, I noticed that the variable template is not consistent for road-transportation.

For some variables, we have an explicit "Road" category, e.g.

• Energy Service|Transportation|Passenger|Road
• Energy Service|Transportation|Passenger|Road|Light-Duty Vehicle

And for others, we only have the vehicle-types LDV, Buses and Trucks separately (see the list here).

• Final Energy|Transportation|Light-Duty Vehicle (without "Road")
• Emissions|CO2|Energy|Demand|Transportation|Light-Duty Vehicle (without "Road")

And for these two variables, there is a parallel distinction into Passenger vs. Freight emissions and energy demand.

Question for me is whether we want to harmonize that? And if yes, in which direction should we harmonize?

[jkikstra]

Would be great to harmonize it.

But also let's not hold up the emissions PR (which would be very welcome already right now; #255) because of the energy variables (where it would be fine to update the reporting in spring I think).