Systems in Focus: Transportation

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Traffic jams are something we all have experienced. It has been observed many times that building more roads (or traffic lanes) to reduce congestion doesn't work in the long run. The demand grows to fill the traffic lanes available. This model looks at that phenomenon: How could it be that more roads do not reduce traffic congestion? Several factors come into play:

• The population is growing so the number of cars on the roads will increase over time.
• There are long delays in planning and building new roads.
• Construction during expansion reduces the number of traffic lanes available.
• When roads become too congested, some people will reduce how much they drive their cars. They will stay at home more, they will ride with friends, or they will use public transportation or other modes of transport (e.g., rail, air). When roads become less congested, they will take to the roads again.

Systems in Focus: Transportation Model

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Many factors contribute to the growth rate of a region but are not included in this simplified model. Instead, the area's population grows exogenously. In addition, while this model includes people voluntarily staying off roads that are too congested, what they do instead, and the resulting impact, is not modeled. Finally, the model’s construction effect only applies to new roads, not road maintenance.