So far, we have a traffic micro-simulation module, and a routing module. The input to all this, apart from the network information, are the trips. However, these trips need to be generated somehow. As a first step towards this, we will consider the question of departure time choice. Let us assume that people want to arrive at work at a particular time. There is a penalty associated with being early (which consists of wasted time), and a penalty associated with being late (which may consist of an angry employer). Also, the travel time may vary depending on when one travels. The idea is that there is a trade-off between these elements. For example, if the travel time is much shorter when traveling early, people may accept being early in spite of the waste of time. This is in particular true if one has a time window to start work, and the only argument against starting early is that one has to get up early.