How many times blocked in the middle of the traffic We thought that to improve circulation it would be necessary to add new roads? In reality, more roads do not necessarily mean less traffic: sometimes close some It is the choice improve. This counterintuitive phenomenon is called Braess paradoxfrom the name of the German mathematician Dietrich Braess who described it in 1968. This paradox is a well -known principle to those who deal with urban planning and one of the most famous cases occurred in Seoul, South Korea, when the closing of a highway Six lanes led to a traffic improvement internal and outside the city. All this, of course, without there being a decrease in circulating cars.
What is and why the Braess paradox happens
Braess’s paradox says that increase the number of roadsif traffic is not regulated, it can worsen circulation. Closing some of them, on the contrary, can make the journey faster. In other words, adding a road to the road network can paradoxically slow all. But how is it possible? Let’s see it with an example.
Let’s imagine we have to go From point A to point b. To do it, we have two roads: the north, in which there is a very short stretch on a narrow road and then you enter the highway and the south one, where there is first themotorway And then one narrow road. If there is no traffic, we will use 45 minutes To go from point a to to, whatever the road we choose. Both sections of the highway, in fact, require us 35 minutes and both strokes of narrow road require 10 minutes, if there is no one around.
The situation changes, however, if we find ourselves traveling these roads during therush hour. In this case, the traits of motorway they do not suffer the increase in traffic and continue to last 35 minuteswhile the traits on narrow roads they will require Much more timebecause slowdowns will be created. In particular, travel times will increase of (number of machines)/10. So, if there are another 100 motorists, we will put 10 (= 100/10) more minutes, if there are 300, we will put 30 (= 300/10) more minutes and so on.
If in total there are 200 people That they must travel this route, in the long run the situation will stabilize with 100 people traveling the north and 100 stretch that travel the south. In this way, each motorist will take 35 minutes on the highway and about 20 minutes (10 minutes “standard” plus 10 minutes due to traffic) on the narrow road, for a total of 55 minutes.
At this point, we think that the municipal administration decides to open a “shortcut”That connects the two shorter stretches, that is, those on the narrow roads. This shortcut will be very wide, so as to always guarantee the passage in 5 minutes. If we did this new path of Nightwith none around, to go to A A B we would put ourselves 25 minutes (10 minutes for each stretch on the narrow road plus 5 minutes on the shortcut), and we would have actually spared some time. The problem takes place during the top hour.
Over time, All 200 motorists who have to go from to B during the top hour they will notice the shortcut and they will decide to take it for Try to save time. In doing so, however, they will carve the narrow roads causing strong slowdowns, up to 20 minutes more. We then arrive at paradox: before having the shortcut, to go from the point TO point B in moments of worse traffic It took 55 minutes; After adding the shortcut, however, they need 65 minutes (30 minutes for each stretch on the narrow road plus 5 minutes on the shortcut). 10 minutes more than when there was no shortcut.
This paradox happens why each motorist thinks only To what is good for itselftherefore trying to travel the fastest road, but in doing so creates one disadvantageous situation for everyonealso for himself.
Close some roads improves traffic
This paradox may seem very far from reality, and instead It happens more than we imagine. Closing some roads can actually improve circulation and open others can worsen it.
For example, in 1990the transport commissioner of New York He decided to close the very busy 42nd road for the day of the earth. Many feared chaos, but the exact opposite happened: traffic improved significantly. The same thing happened in 2010when the mayor forbade the circulation of vehicles on some sections of Broadway. Also in that case the traffic flows were distributed better and the safety of pedestrians increased.
We have examples of this phenomenon in every part of the world. TO Seulin South Korea, the demolition of the gigantic Cheonggye Expressway highway has made the traffic much more flowing. A similar phenomenon happened to Stuttgartin Germany, where they had to close a stretch of newly built road to traffic, because the situation worsened instead of improving it.
The phenomenon of Braess paradox has been widely studied by those who deal with urban planning and it has been seen that it can be attenuated by reducing the individual choices that damage the community. Tolls, bollards, limited traffic areas and navigation systems that take into account real -time traffic are some of the tools that help to limit their effects.
