Topic: Transport - stock turnoverSubscribe | Previous | Next
Tomislav Čop 3/24/2022
Hello!
I am modeling the transport sector using the stock turnover method, so I have two challenges that I am trying to solve:
1) if I use the top-down method, after branching out several categories of traffic then it is no longer possible to enter "stock" anywhere (I checked by clicking on each folder / category). Are there any restrictions that might confuse the tool?
2) If I do not use the top-down method, I determine the projections of the future vehicle stock based on population projections and car ownership factor. So, in the variable "sales" I should enter the calculation of the difference between the target stock and the current stock in a given year. However, LEAP does not allow such referencing. I tried to make an additional user variable but failed.
Does anyone have an idea for help?
Charlie Heaps 3/24/2022
Hi Tomislav,
In the top-down approach you enter stock values only at the highest level demand branches (and only for the base year of your model). You than enter values in the stock share variables which allocate those high level stocks down to the low level technology branches (shown as a tire icon in the tree) . Similar with sales/sales share variables. In the bottom-up approach you simply enter stock and sales values down at the low-level technology branches for both variables. Both methods do the same calculations, they differ only in how you specify the input data.
Sales is the number of new vehicles put on the road in a particular year and note also that the stock in the base year is measured at the start of the year (i.e. not including the base year sales).
You only need to enter stock values for the base year. Future stocks are calculated base on future sales and the internally calculated retirements. In other words, the stock variable is just used to initialize the model in the base year. The retirement schedule is derived from the data you enter describing how the base year stock is split among different vintages (via the Stock Vintage profile selection box) as well as the information on how long vehicles last (the Survival profile selection box).
It is also possible to make sales a function of the internally calculated Retirements value. For example, you could write an expression for sales like this 1000+Retirements. In this way, the stock would increase by 1000 in each year, while also replacing any retired vehicles. You could use that if you want to try and achieve some target stock.
More info here: https://leap.sei.org/help/Demand/Stock_Analysis.htm
I hope this helps.
Charlie