Induced Demand
PREDICTED TRAFFIC AND ACTUAL TRAFFIC AFTER A ROAD WIDENING
by Wes Marshall
You already have a congested roadway, and the transportation planners predict even more traffic on that road in the near future. What do you do? For most of the last century, the answer was to increase capacity. In the short-term, this seemed to work. Time and time again, over the long-term, the actual amount of traffic after the capacity increase grew far more than expected. What seemed like an obvious solution to a congestion problem continued to disappoint. But why?
The reason for these failures lies with the principle of induced demand. Once capacity increases, not only do you get the originally predicted traffic growth, but you also facilitate some often unanticipated changes in travel behavior. First, existing road users might change the time of day when they travel; instead of leaving at 5 AM to…
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Utopia, you are standing in it! 
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