Mathematical models are used to estimate the impact of changes before they are implemented in reality. For example, transport models can be used to estimate the impact of a new ring road before it is actually built. Impacts that can be assessed include, for instance, traffic volumes, travel times or noise.
Such models help estimating impacts of infrastructure projects and policies in advance. They can also help to optimize plans to help achieving planning goals. Sometimes, models are also used to test the effect of global trends, such as rising energy prices, migration or climate change.