Improving equation

[sya_ouniversity]

I want to model the effects of traffic. For the growth of vehicles I’ve used historic data to estimate the yearly growth rate. This looks good, but as unlimited growth is not realistic I now put a at a motorization rate of 850 vehicles per 1000 inhabitants. I used the following equation for this: IF THEN ELSE(("motorization rate">850), 0.01, [growth rate variable]).

Is there a better or more sophisticated way to do this? Or is this fine?

Thank you!

[Administrator]

I'd make a couple of small changes first. Putting numbers into equations is generally considered bad practice as anyone looking at the model will have no idea what they are.

MAX MOTORIZATION RATE = 850 (Units:car/kperson)
GROWTH RATE WHEN MAX MOTORIZATION ACTIVE = 0.01 (Units:DMNL)

IF THEN ELSE("motorization rate" > MAX MOTORIZATION RATE, GROWTH RATE WHEN MAX MOTORIZATION ACTIVE, [growth rate variable])

This allows you to change the rates, plus give them proper units so you can check the dimensional consistency of your model.


I'd be inclined to have a S curve instead of the "0.01" you have. Work out the percentage of population with cars, as that gets closer to 100, the growth rate slows down. If you have a constant (0.01), the rate will rise linearly, that's probably not what happens in reality. Saying that, if you just need a quick idea of the behaviour, what you have will do.

[sya_ouniversity]

Thank you! That makes absolute sense. I will also look into making an S curve.