Ralph Samuelson 1/19/2011

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We would like to build a model using Transport Analysis where we can specify the size of the vehicle fleet each year (as a function of population). Sales each year should therefore equal the growth of the fleet (a function of the growth of the population) plus replacement vehicles. Replacement vehicles should equal the number of vehicles being retired, as calculated by LEAP using the lifecycle profiles. Is this possible?

If this is not possible directly, do you have any suggestions for good work-arounds? It seems very limiting to have to exogenously specify sales of vehicles when we have no idea how many relacement vehicles will be needed, and therefore no idea what the implications of our sales assumptions will be on the total size of the fleet.

Thanks, Ralph

Charlie Heaps 1/20/2011
 

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>>We would like to build a model using Transport Analysis where we can specify the size of the vehicle fleet each year (as a function of population). Sales each year should therefore equal the growth of the fleet (a function of the growth of the population) plus replacement vehicles. Replacement vehicles should equal the number of vehicles being retired, as calculated by LEAP using the lifecycle profiles. Is this possible?

Hi Ralph,

Sorry for my slow reply. I have good news and bad news for you. The good news is that this is basically possible. In the SALES variable you can specify an equation so that SALES are a function of retirements. To make them equal, just write the word "Retirements" in the place where you specify sales. Alternatively if you want sales to be 10% more than retirements, specify "Retirements * 1.1"

I have posted a simple example of this in area named 'Sales Equals Retirements" You can get it from the Area: Install: Install from Internet menu.

The bad news is that there seems to be a bug in the stock turnover calculations, so that even if you set them equal the stock seems to decline slowly. I need to investigate why this might be. Those turnover calculation are one of the more complex parts of LEAP so it might take me a while. I suspect there is an issue in how LEAP treats stocks in the first scenario year of the calculation.

Best,

Charlie

Ralph Samuelson 1/21/2011
 

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Thanks, Charlie! This information is very helpful. We'll try it, and let you know anything we learn about the bug. Regards, Ralph

Ralph Samuelson 2/8/2011
 

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Hi Charlie,
There appears to be a bug here other than the one you mention.
Whenever I try to put the word "Retirements" into an expression for SALES in the expression builder, I get an error message that says "Stock vintage profile must be zero in year zero". The message is obviously spurious, as I get it only if I type in the complete word "Retirements" (not any portion thereof!), and because my stock vintage profile does have a zero in year zero and I don't get this error message any other time.
For this reason, I am not even able to enter an expression containing the word "Retirements".
Any advice?
Ralph

Charlie Heaps 2/8/2011
 

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Can you send me your data set so I can take a look? Send to leap@sei-us.org

Thanks!

Tory Clark 2/9/2011
 

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Hi Ralph,

Thank you for sending your dataset. For now the approach that you are describing only works for bottom up stock methodologies. You can fix this by going to General: Basic Parameters, clicking on the Stocks tab and unchecking the "Top-down sales and stock data" option.

Best,

Tory