But, yes! It's absolutely amazing what goes into modeling traffic as accurately as possible. When we expanded to model pedestrian traffic as well, we even went so far as to build a mock store.
It's fascinating to see how small changes can influence traffic and alter the throughput. Simple things, like frequency of signage has a large impact. There are also regional differences where whole regions will, as an average, drive very differently.
You can run all the models, collect all the data, and someone will still get drunk and reverse the wrong way on a one way street. You'll never get perfect predictions and so there are constant changes being made. That kept it interesting.
What I worked on was all proprietary. It'd be interesting to see an open source project in this arena.