08/05/2026
THE SCIENCE OF WIDENING ROADS CAUSING MORE TRAFFIC
Induced demand is more than a theory. It is a reliable observation, and is best seen with the expansion of road capacity. The prevailing belief is that road expansion results in improved traffic, as driving no longer feels like a frustrating and slow ordeal. Relief is believed to be part of the success of the expansion, yet it is only temporary. Road capacity, once expanded to the additional driving, causes longer trips, and changes the developmental patterns of driving, leading to a shift away from walking, cycling, and public transit. Eventually the volume of traffic causes road capacity to become congested once again, and likely more so than originally.
This is a result of travel behavior reacting to the perceived cost of travel.
Wider roads result in a decreased cost of travel. People that once avoided peak-hour driving begin driving again. Travel becomes more routine. Households make decisions about where to live, work, and shop based upon the knowledge that driving will be convenient. This results in a clear message that more road space creates more driving.
This relationship has remained constant with expanded road and increased driving, as shown by the decades of research on the transport of different continents. This driving is especially elevated in urban areas.
A Care-Centric approach recognizes the public health burden of widening roads. The care-centric approach is respond to the cause and not the symptoms.
If an over-reliance on cars is demonstrated by traffic congestion, adding more lanes is guaranteed to worsen dependence. However, investing in reliable transit, safe walking, and cycling, along with compact land use, all combined with demand management, gives people real alternatives and ultimately reduces traffic congestion, along with being far more effective than the continual expansion of road capacity.
Induced demand encapsulates a simple idea.
Designing car-centric cities leads to having more cars. Designing around people, as well as health and care, makes traffic something we actively manage rather than something that grows without limit.
Road widening does not fail by mistake.
Widening roads does precisely what it indicates: the more roads that cars can use the more cars there will be to use them.
Source: https://www.tomtom.com/newsroom/explainers-and-insights/induced-demand-explained/