Traffic congestion is partly a result of infrastructure planning and development, but mostly it is a symptom of economic growth.
Infrastructure development is not dynamic – capacity is built to accommodate a certain threshold at one time; once that threshold is reached, congestion occurs. Demand, however, increases according to a variety of factors beyond just the road capacity and the economy is a major driver. As the economy grows and more people can afford to buy cars, the roads slowly fill up. Increasing road capacity is, on its own, an ineffective way to combat congestion because you are not really addressing the root cause of the congestion, just a symptom. Therefore, the quickest way to solve a city’s traffic congestion is, in fact, to kill the economy so fewer people can afford to drive (that’s a bit extreme I guess, you could just make it more expensive to drive through taxation).
For less quick, more sustainable solutions, one needs to consider the principle of the triple convergence (increasing road capacity = more cars due to economic growth + more people now taking the improved road during peak hours who had previously shifted to off peak hours to avoid congestion + more people now taking the improved road who used to take other forms of transportation to avoid congestion = more congestion). Congestion needs to be addressed as part of a systemic upgrade of the entire transportation network, not just a single component of it.
However, as I mentioned above, demand is continuous and dynamic and infrastructure development is not. Congestion is, therefore, the point of equilibrium on the demand/supply graph, and no matter what a city does, economic theory says that equilibrium will always occur. As a result, congestion is inevitable. It is better to manage congestion than to try to “solve” it.
Originally submitted to Quora on April 23, 2015.