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Latent demand and induced demand: How to uncover the mystery behind traffic flow?
The concept of induced demand is often hotly debated in transportation planning, especially in debates over expanding transportation systems. Among them, induced demand describes the phenomenon of rising demand caused by increased supply, which means that with the expansion of transportation infrastructure, new drivers quickly fill the newly expanded roads, causing new congestion. This makes people wonder, how can we break this cycle and find more effective transportation solutions?
"More roads won't change the fundamental problem of traffic flow and may actually cause more congestion."
According to research, "induced demand" refers to the phenomenon that when transportation supply increases, the accompanying transportation demand increases accordingly. This theory originated in the early 20th century and has received attention from many fields including politics, economics and sociology in the past few decades. Debates about transport expansion often involve a complex mix of components, such as people's travel habits and psychological responses, which can cause new roads to quickly fill up with traffic.
According to CityLab, induced demand is an umbrella term for the various interactions that explain why new roads reach saturation quickly. There may be significant latent demand in rapidly growing areas where many roads were not originally designed to accommodate current population numbers. Many highways will see a surge in drivers immediately after new lanes are opened, ultimately causing congestion.
“Latent demand is often a demand that cannot be realized until new infrastructure emerges.”
The concept of latent demand raises several key questions: Does past demand still exist during transit expansion? Does the impetus for change come from a shift in transport modes, such as from public transport to private cars? Perhaps this is an issue that urban planners need to think deeply about.
Based on historical analysis, the potential demand has been recognized for many years. It was once called "transportation generation," a hidden need that was not fulfilled because of inadequate infrastructure. As early as the 1930s, electric railroad executives in St. Louis pointed out that widening roads would lead to increased traffic. And in New York, the highway-building program of famed “Big Builder” Robert Moses ultimately proved that expanding roads not only failed to reduce congestion, but actually had the opposite effect, leading to congestion problems on three bridges.
"Expanding highways without a balanced transportation system will not fundamentally solve traffic congestion."
However, the opposite of inducing demand is so-called "reducing demand." This phenomenon is also worthy of attention in transportation planning, because people's behavior patterns will adjust due to changes in the traffic environment. For example, when new transportation options become available, some drivers may choose alternative modes of transportation or travel during off-peak hours.
According to the study, additional short-term traffic can come from two sources: diverted travel and induced traffic. Diverted travel refers to people changing routes to avoid rush hour, while induced travel refers to new car trips that occur when road travel costs fall. All of this points to a common conclusion, that is, there is a lasting and interactive relationship between road construction and traffic demand.
From a policy perspective, while many planners take into account future traffic growth, this growth calculation does not necessarily reflect the induced traffic created by new roads. This results in the expansion of new facilities often failing to effectively respond to immediate traffic needs.
"We can't just keep building roads indefinitely because we need them."
In response to current traffic challenges, some cities, such as Bogota in Colombia, have chosen to invest in bicycle infrastructure. This approach not only encourages citizens to choose more sustainable travel methods, but also effectively reduces traffic congestion and carbon emissions. In contrast, traditional road construction seems to always repeat the same pattern, but it may not help solve the increasingly serious traffic challenges.
Looking to the future, transportation planners cannot rely solely on expanding roads to meet transportation needs, but also need to conduct more comprehensive thinking and planning. As urbanization accelerates, should we examine the relationship between induced demand and potential demand and seek more effective solutions to get rid of this seemingly endless cycle of traffic problems?
