Understand Induced Demand
TRAFFIC ENGINEERING THEORY is straightforward: a street is congested because the number of drivers exceeds its capacity. If you enlarge the street, you will eliminate congestion. Unfortunately, seventy-five years of evidence tells us that this almost never happens. Instead, what happens is that the number of drivers quickly increases to match the increased capacity, and congestion returns in full force. It’s called induced demand. These new drivers are the people who were taking transit, carpooling, commuting off-peak, or simply not driving because they didn’t want to be stuck in traffic. When the traffic went away, they changed their habits. Maybe they even moved farther away from work, as the time-cost of their commute went down. Unfortunately, thanks to them and others like them, this honeymoon couldn’t last long.