1. What is induced demand?
Induced demand is a concept from economics: as supply increases and incurred costs decline, demand will increase. This phenomenon has been widely observed and studied in transportation systems where highways have been expanded to alleviate road congestion problems.
2. How does the concept of induced demand work in transportation systems?
As highways become congested due to population growth and increased usage, or as transportation agencies plan for anticipated population growth, highways are expanded. This includes widening roads and adding new traffic lanes to increase capacity and manage congestion. Generally, these expansion projects ease congestion in the near term. However, the benefits do not last. Instead, travel demand grows proportional to the added capacity.
Highway expansion projects typically follow the same patterns. The increased road capacity created by the new added lanes eases congestion and reduces the costs associated with travel times. The eased congestion attracts additional drivers to use the roads. Some of the new drivers include people who would have previously met their travel needs using other roads or alternate modes of transportation to avoid the congested highway. Other new drivers arise from the urban sprawl made possible by the expanded highway.
Over time, highway usage continues growing until the congestion benefits created by the expansion disappear altogether. Then the cycle starts over again, and new highway expansion projects are planned to, once again, ease the congestion problems—and their related impacts such as air pollution—that have now returned.
3. What are the consequences of road expansions?
Road expansions do not ease road congestion in the long run. The evidence shows that, ultimately, they make traffic and pollution worse as short-term congestion relief is usually offset by increases in driver usage of the expanded roads within 5–10 years. But there are other consequences as well:
4. What are alternative strategies for addressing road congestion and the transportation needs of a growing population in a region?
Many alternative transportation strategies exist for addressing road congestion and the increasing transportation needs of growing populations. Collectively, they support a broader concept known as traffic demand management, which is the application of strategies and policies to reduce travel demand or redistribute it in space and time. When used together, these strategies can provide the long-term solutions to transportation challenges that freeway expansions only deliver in the short term. Some key alternative strategies include:
5. What is a Metropolitan Statistical Area (MSA)?
A metropolitan statistical area (MSA) is a core geographical region in the United States containing a city (with a population of at least 50,000) and adjacent communities that are linked by social and economic factors. MSAs are defined by the United States Office of Management and Budget based on Census Bureau data.
6. What is the source of the VMT data used by the SHIFT Calculator?
The SHIFT Calculator utilizes existing lane mileage and VMT data from the Federal Highway Administration (FHWA).