The notion that widening roads eases congestion is a myth.
We’ve had the evidence for a century and cities have proceeded as if they didn’t know. In the process, much that’s good about cities – their charm, strong communities, convenience, safety, economic stability – has been eroded. It would be no exaggeration to say that much of what separates great and poor cities depends on how they’ve handled congestion.
There is ample evidence demonstrating why road-widening doesn’t work as a congestion-reliever, what road-widening actually achieves, and how congestion should really be addressed.
Road widening is not the magic pill to ease congestion. In fact, widening roads to reduce congestion is worse than doing nothing.
One might assume that a wider road allows traffic to flow more efficiently by distributing the same number of vehicles more space. But, this argument is flawed: when roads get wider more people start driving or reverting to the now wider road from alternate routes they have been using - a phenomenon known as “induced demand*”. People drive when they used to bike, walk, or take public transit; they move farther away from their jobs in town and drive farther to get there; they drive in rush hour when they used to drive at other times; and businesses that depend more on roads will relocate to cities, bringing more truck traffic with them.
*Induced demand means that for every person that switches from driving to an alternative, another driver will take their place.
No longer can road widening be justified as a congestion-easing tool. Road widening lengthens commutes, increases household costs, worsens pollution and harms the economy.
Another big problem for urban areas is the flooding that can occur when heavy rains fall over a city. Since runoff from an acre of pavement is about 10–20 times greater than the runoff from an acre of grass, the increased paved surface from road widening makes the surrounding neighbourhoods more susceptible to flooding.