Road wideningand traffic congestion Part 2 - Road congestion paradox

Building more roads or lanes induces more traffic and will not address congestion! This is counterintuitive and runs contrary to supposed common sense. But traffic congestion in urban areas cannot be addressed by common sense. Transportation is a science and it gets more complex the bigger your city is.

Let's try to look at congested roads and what happens when you add more lanes. I would like to paraphrase the analysis shown in a Wendover Productions video in YouTube entitled "How to Fix Traffic Forever" (https://goo.gl/TnxxgP). We start off by saying, "Wider roads mean more capacity so cars can run faster." That's a very narrow picture of the issue -you can't just think about one road, you always think of a road network of the city.

Many people choose not to drive places because of how long it takes -traffic congestion simply means less travel speed and more travel time. If the traffic is bad, you can take public transit, wait until a less busy time, or just not travel at all. Some do groceries once a week instead of twice. Others carpool. When a road is expanded (or a lane is added), cars go faster and travel times initially decrease. The number of vehicles suddenly increases because of "induced demand" -people start driving because it's easier to drive. If the capacity of a road doubles, the number of vehicles using that road will also double. If it doubles again, the number will again double. In reality, there's no such thing as an optimum width, area, or number of lanes for a road. More roads mean more cars; less roads, less cars. Drivers will adjust to any change in road capacity.

Then, there's what we call the "Braess's Paradox" which says "an alteration to a road network to improve traffic flow may actually have the reverse effect and impedes traffic through it." The explanation is behavioral rather than technical -by adding extra capacity, the moving entities selfishly choose their route which usually reduces overall performance. It was postulated by German mathematician Dietrich Braess, who noticed that adding a road to a congested road traffic network could increase overall journey time. Plus, there's this tendency of people to buy new cars every time a new lane makes driving easier.

And the opposite is also true. There are many instances of improved traffic flow when existing major roads are closed. In 1969 in Stuttgart, Germany, after building the road network, the traffic situation did not improve until a section of newly-built road was closed for traffic again (source: Wikipedia). In 1990 the temporary closing of 42nd Street in New York City for Earth Day reduced the amount of congestion in the area. And who didn't hear about the Cheonggyecheon River Restoration Project in Seoul, South Korea, where an entire expressway was demolished -surprisingly speeding up in traffic around the entire city. In 2009, New York experimented with closing Broadway at Times Square and Herald Square -these resulted in improved traffic flow!