Time is a limited and valuable resource. As much as possible, people should spend the precious hours of their lives in the most satisfying and productive possible ways. This has important implications for transportation planning, since most people spend a significant amount of time in transport, and travel time savings are often the greatest projected benefits of transport projects such as roadway and transit service improvements.
One of the most widely cited numbers in contemporary transportation media coverage and policy discussions is the cost of congestion estimates that Texas Transportation Institute (TTI) annually produces as part of the Urban Mobility Report series. The 2009 version of that report (http://mobility.tamu.edu/ums/) shows an estimate of the cost of congestion of $87.4 Billion for the top 439 U.S.
I often hear debates over the costs of different modes of transportation, particularly between driving and public transit travel. Rising fuel prices have made public transit more attractive for some trips, boosting ridership, but critics point out that for most trips, transit fares are still comparable with fuel costs (for example, at $4 a gallon, fuel costs about $2 for a typical 10-mile trip, comparable to a bus fare in a typical city), and generally take longer. It is therefore legitimate to ask whether public transit really saves money.