Calculating fuel consumption and emissions is a typical offline analysis step that uses the data previously obtained by simulations or observations. Depending on the aggregation level and level of detail, we distinguish several global, macroscopic, and microscopic approaches. The focus of this chapter is on a microscopic physics-based model with a high level of detail. As a “modal” model, it takes speed and acceleration profiles (as obtained from microscopic simulations or real trajectory data) and the engine speed (as obtained from gear-shift schemes) as input and is parameterized by vehicle and engine attributes. The outputs are, on a single-vehicle basis, instantaneous fuel consumption and emission rates ( \(\text{CO}_2\) and others). Because the presented model is based on energy flows, it is also straightforward to apply it to battery-electric or hybrid vehicles. There, the inputs are the speed/acceleration profile and the temperature and the outputs the required charging energy, the range, and indirect \(\text{CO}_2\) emissions. To what degree does traffic congestion increase fuel consumption? Under which conditions are roundabouts more environmentally friendly than signalized intersections? How much \(\text{CO}_2\) emission can be saved by novel intelligent traffic systems? Why is the range of electric vehicles so much reduced when driving on highways or in the cold? These are typical questions that such models—in connection with microscopic traffic flow models—can answer.