Why do some traffic jams come out of nowhere?

New Year's Eve, parties, holidays, crowded roads and many people who travel will know very well what they will face: a lot of traffic on the highways. This is quite common. After all, the volume of cars on the roads is immensely higher during this period. When it comes to cities, peak periods for the rest of the year remain early in the morning and late in the afternoon.

In some metropolises, however, traffic can happen almost all day long, depending on the region. However, there is often no reason for traffic to stop both on the road and in the city; There is no lengthy traffic light, no accident or road works. Even so, everything stops “out of nowhere”, forming a congestion dubbed “ghost”.

Minutes later, traffic starts flowing again and everyone moves at normal speed. But why does this happen? According to an article by Joseph Stromberg of Vox, a number of different groups of researchers have been using mathematical calculations and real-world experiments to try to answer this question, reaching some conclusions.

An example can be commonly observed: when there are enough cars on a highway, any minimal flow interruption can cause a chain reaction. Thus, if a vehicle brakes slightly and the rear also brakes to avoid crashing, this simple reduction eventually increases until it produces a slow or slow traffic wave.

Waves

"These traffic waves result from minor disturbances in a smooth traffic flow, such as a road collision or a driver's braking after a moment of inattention, " Temple University mathematician Benjamin Seibold told Vox. .

You may be thinking, "OK, but when the cars leave this main lane, this traffic wave disappears." Well, unfortunately not. According to the researchers' analysis, even when cars leave this wave of traffic, it does not disappear: it gradually extends backward against the direction of traffic.

"Typically, these waves are 100 meters to one kilometer long, and usually start with vehicles running at a sudden increase in density at the beginning and a subsequent drop in speed. Then, after that, they slowly accelerate again, " he said. researcher Benjamin Seibold.

The expert and a few other research colleagues developed the concept of these waves - which they call jamitons, because they are analogous to waves in physics called solitons - using computer algorithms that simulate driving behavior. See below:

Some Japanese researchers also conducted research that reached the same conclusion. In one experiment, they instructed 22 drivers to drive at the same speed and to preserve the same amount of space between cars on a small circular road. Inevitably, waves of traffic formed. Curious that, no?

Is there a way to avoid?

Probably people are likely to blame others, considering that the traffic jam is the fault of those who drive badly. But that is not the point.

The models studied show that traffic jams that form suddenly are easier to come by when people drive as fast as possible and need to brake quickly so as not to hit the front car, which causes the chain reaction we talked about above.

But how to avoid this reaction? Researcher Benjamin Seibold gives a hint: "If people look ahead at the higher traffic densities ahead and let their feet off the accelerator first, they also leave more space in front of them - instead of waiting until they really need to brake - this can prevent jams from appearing. ”

It sounds easy, but in practice it is not so much and researchers are aware of it too. "The models show that even when all drivers drive by the same exact rules, and no one does anything wrong, those waves can still come, " Benjamin said.

However, there are some conditions that engineers can bet on to reduce these traffic jams. For example, it is known that the straighter and smoother the road, the less likely traffic jams are to form, as this also means that drivers will not have to do such sudden braking.

Another idea is variable speed limits where they can be lowered in the areas most likely to get into "ghost" traffic jams, causing cars to slow down instead of all at once. In some cases, this action could break the waves of slow or stopped traffic.