🧵 11/? With Travel Demand Modeling (TDM), Steps 1-3 compute the Origin-Destination (OD) matrix of trips. That's where the junk science happens. Most of it is in Step 1: Trip Generation.
Approaches to Step 1 vary. In South Africa and the UK, we averaged traffic growth over a period of some years, or sucked a defensible number out of the air. We just assumed existing traffic would grow at somewhere between 2-8% depending on the rate of development in the area. The US method is more complicated.