In addition to understanding user value for different types of trips, it is crucial to understand the relationship between prices and quantity of travel, which can be rep- resented by travel demand curves (see Box 4). For exam- ple, some people might choose a home that requires very long commutes if the costs associated with that com- muting are low. Similarly, if vehicle travel prices are low, people will use car for trips that could easily be made by other modes, and will drive alone for urban trips that could be made efficiently by public transport.