Why Do We Keep Widening Highways If It Doesn’t Reduce Traffic?

Induced Demand

The concept of induced demand explains why highway expansions often lead to increased traffic congestion rather than alleviating it. Megan Kimble highlights that adding lanes to highways creates more capacity, which in turn attracts more cars, ultimately worsening traffic conditions 1. This phenomenon has been recognized since the early 1960s, demonstrating that increased supply leads to higher demand as people adjust their commuting habits, such as moving further from work or taking more trips.

When you add capacity to a highway in the form of new lanes, more cars will rush to fill up that capacity.

--- Megan Kimble

This counterintuitive outcome challenges the effectiveness of highway widening as a solution to traffic congestion and raises concerns about its environmental impact, including increased greenhouse gas emissions 1.

   

Case Studies

The Katy Freeway in Houston serves as a prime example of induced demand, where expansion led to worse traffic conditions. Megan Kimble describes how the freeway, expanded to 26 lanes, saw increased rush hour travel times within five years 2. Local activists, aware of these issues, have been working to halt further expansions, such as the I-45 project, which threatens to displace residents and consume significant land.

The Katy Freeway is like the textbook example of induced demand.

--- Megan Kimble

These efforts highlight the community's understanding of the limitations of highway expansions and their willingness to challenge projects that exacerbate traffic and environmental issues 2.