Traffic evaporation is a phenomenon that has resulted from strategic removal of road space previously dedicated to motor vehicles. This is not the expected result. Imagine improving traffic flow by closing roads or lanes to cars! By recognizing this phenomenon and understanding the necessary factors to reach traffic evaporatation, some progressive cities around the world are enjoying a reduction in traffic as they transform these sequestered public spaces back into places for people to play, shop, relax and connect.
The European Commission is one of the first agencies to formally recognize and demonstrate this phenomenon in their 2004 report: Reclaiming city streets for people — Chaos or quality of life?
One of the most profound examples of reclaiming streets for people is taking place all across New York City. Make sure to click through this slide show of changes along Broadway and take a look at this video that highlights their experience with traffic evaporation:
New York City is only one of several U.S. cities taking bold steps toward reclaiming space for their citizens. San Francisco recently carved a public park out of one of their most dangerous intersections. Watch this video for the inspiring story:
Disappearing Traffic? is a civil engineering peer journal paper that examined 70 case studies and included input from over 200 transportation officials worldwide with surprising results.
This academic paper explains some of the factors that must be considered when striving to acheive traffic evaporation: Price of Anarchy in Transportation Networks: Efficiency and Optimality Control
Mentioned in the above paper is the Braess' Paradox which is a factor in some cases of Traffic Evaporation. In the 1960's, German Professor Dietrich Braess discovered that adding capacity to a network that allows selfish choice by the users (such as our roadway system) can sometimes reduce the performance of that network. Those of you who have seen the movie "A Beautiful Mind" are familiar with the Nash Equilibrium that taps the tendancy for selfish choices. Braess discoved that the Nash Equilibrium in networks such as our roadway systems is not actually optimal for performance. This paper also does a good job of explaining: The Braess Paradox
For another viewpoint away from the benefits of traffic evaporation for easing traffic congestion, read this article: How Traffic Jams Help the Environment. So let's look at reclaiming public space from traffic lanes knowing that many times traffic evaporation will occur and if it doesn't, well that's a good thing, too.
Freeway removal is the most dramatic means of reducing dedicated motor vehicle space. Some of the more famous freeway removals in recent years have taken place in downtown San Francisco (resulting from earthquakes), the Chattanooga Riverfront, Milwaukee and along the Seine River in Paris (resulting from a mayor's project). This web site offers links to these and similar stories as well us proposed freeway removals around the world: http://www.preservenet.com/freeways/index.html
This recent article highlights the struggle for a proposed freeway removal in Boston,