Dr. Andrew Farkas Demands Correct Use of Terminology
Language and understanding often limit public discussion of cities and urban transportation. Even academics across disciplines don't use the same terminology, but one term has been prominent in the media lately - but used incorrectly. Some articles credit traffic congestion to the "induced demand" from the building of new roads or additional lanes on existing roads. "Induced demand," as used in the articles, is a variant of "supply creates its own demand," attributed often to the marketing of new products or services that didn't exist before. But supply does not create demand. Demand already exists. Besides, supply of road space is certainly not a new product.
The authors are actually describing "induced traffic" or increased consumption of road space by motorists. Economic theory tells us that consumption and the prices regulating it are determined by supply and demand. High demand during peak hours of urban commuting and goods delivery may exceed the capacity of road space, resulting in increased consumption and traffic congestion despite high prices, time spent and out-of-pocket costs. If road space is added, the price of travel decreases. Lower prices for travel encourage more consumption of road space. If capacity is again exceeded during peak times, then congestion reoccurs. So, yes, congestion can reoccur, but not because demand has been created or induced by road space, but because lower prices encourage more consumption (induced traffic).
Some individuals describe this process of congestion, adding road space, and eventual reoccurring congestion as leaving us back where we started, but that's definitely not the case. Induced traffic means that the lower price has enticed existing motorists and new ones to travel more to economic opportunities-a beneficial result. Also, free-flowing traffic may occur, at least for a while. Demand could expand over time because of population and economic growth, which could increase the base level of traffic congestion.
Now, the solution to our traffic woes is not adding road space automatically when congestion occurs; the economic, environmental and societal costs have been shown to be too great. Instead, traffic congestion should be managed through road pricing and other demand management techniques to move some traffic to off-peak times and other modes. Some judicious adding of road space to obvious "bottlenecks" in the network should also take place.
If we are going to make appropriate investment decisions, it's important for the traveling public to understand the economic forces and travel behaviors that occur in our transportation systems. It's also incumbent upon those of us informing public policy debates to use terms that convey concepts accurately so that we can reach that understanding.
Dr. Andrew Farkas is the director of the Urban Mobility & Equity Center and the National Transportation Center, which are both located at Morgan State University in Baltimore.