Chapter 2: Congestion and Its Extent

“You’re not stuck in a traffic jam, you are the jam.” – German public transport campaign (Kay, 1997)

Congestion—both in perception and in reality—impacts the movement of people and freight and is deeply tied to our history of high levels of accessibility and mobility. Along spatial and temporal dimensions, traffic congestion has been around since ancient Rome (Downs, 2004); it wastes time and energy, causes pollution and stress, decreases productivity and imposes costs on society equal to 2–3% of our gross domestic product (GDP) (Cervero, 1998). In terms of technology, it was noted that an automobile is “a conveyance which is capable of moving 1.6 km (a mile) a minute, yet the average speed of traffic in large cities is of the order of 17.7 km/h (11 mph).” (Buchanan, 1963). For 2002, it was estimated that congestion “wasted” $63.2 billion in 75 metropolitan areas during 2002 because of extra time lost and fuel consumed, or $829 per person. (Schrank and Lomax, 2004) Some refer to these kinds of estimates as misleading since the prospect of eliminating all congestion during peak periods is “only a myth; congestion could never be eliminated completely.” (Downs, 2004). While some research emphasizes that “rush hour is longer than an hour in the morning and an hour in the evening and few people are ‘rushing’ anywhere,” others say that “gridlock is not going to happen because people change what they do long before it happens.” (Garrison and Ward, 2000) Some view congestion as a “problem” that individual drivers are subject to, while others emphasize that the users of transportation networks “not only experience congestion, they create it.” It has been shown that most people make travel decisions based on an expectation of experiencing a certain amount of congestion; while “few consider the costs their trips impose on others by adding to congestion.” (Mohring, 1999) The objective of this chapter is to discuss current definitions of metropolitan traffic congestion and ways it is currently measured. In addition, the accuracy and reliability of these measures will be described along with a review of how congestion has been changing over the past few decades.