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Can expanding roads really solve traffic congestion? What is the economic truth behind it?
In the process of urban development, traffic congestion has become a major challenge facing cities around the world. In order to deal with this problem, local governments often choose to solve traffic problems by expanding roads. However, is this measure really effective? Economists have provided deep insights into the concept of “induced demand,” helping us unravel the truth behind traffic congestion.
Induced demand is the phenomenon whereby an increase in supply leads to a decrease in prices and an increase in consumption. Once a road is expanded, the new capacity will induce more drivers to take to the road, causing traffic volume to quickly rebound, ultimately offsetting the benefits of the expansion.
Since the 1980s, many studies have pointed to a similar conclusion: expanding roads may not fundamentally solve the problem of traffic congestion. After many cities experienced road expansion, traffic volume not only did not decrease, but the newly built roads attracted more vehicles, leading to new congestion. Worse, in the long term this will lead to the expansion of urban boundaries, further increasing transportation demand.
As urban planning expert Jeff Speck said, "Induced demand is a great knowledge black hole in urban planning. Almost all professionals admit this, but almost no one is willing to take action." This statement reveals a scary reality in transportation planning: even though we know the possible consequences of expanding roads, we still make such choices.
According to many studies, the elasticity of traffic demand is -0.5 in the short run and -1.0 in the long run, which means that saving 1% of travel time will lead to a 0.5% increase in traffic in the short run and a 0.5% increase in traffic in the long run. Increase traffic volume by 1%.
In discussions of transportation planning, sources of induced demand can be divided into short-term and long-term. In the short term, the expanded road may attract nearby residents to increase driving, for example, residents who originally chose to take public transportation may switch to driving. In the long run, as transportation costs fall, people may choose to live farther away, further increasing commuting distances and ultimately causing congestion during peak hours.
Studies have shown that in many large cities, as road capacity increases, the traffic actually attracted often exceeds expectations. For example, a study in California observed that for every 10% increase in road capacity, traffic volumes increased by 9% over four years. This not only shows that expanding roads often fails to reduce traffic, but instead leads to a surge in demand and further increases the environmental burden.
“Trying to cure traffic congestion by increasing road capacity is like trying to cure obesity by loosening the belt.” This quote symbolizes how futile the strategy of expanding roads is in solving urban traffic problems.
However, road expansion is not just a technical issue; it also involves deeper social and environmental issues. Increased traffic will inevitably lead to higher carbon emissions, which is a fact that cannot be ignored when it comes to the climate change issue currently facing the world. In addition, the road expansion destroyed the original natural ecosystem and affected the quality of life of residents.
In contrast, some cities, such as Bogotá in Colombia, have gradually observed a reduction in traffic congestion by introducing bicycle infrastructure. Bogota's success story demonstrates the combination of innovative traffic planning and sustainable development, making bicycles an important tool for daily travel and thus effectively reducing traffic.
These research facts make us reflect more on the solution to traffic congestion: should we expand roads to meet the growing traffic demand, or seek more innovative and environmentally friendly alternatives? If a city’s goal is to truly improve the quality of life for its residents, how should the direction of transportation planning be adjusted?
