When there is a traffic jam, what is the first car doing?

The Spring Festival holiday is over and it is the peak season for returning home.

During peak hours, you may encounter a traffic jam. You drive two hours and travel two kilometers. Five hours have passed in eight hours, and there are still eight hours left. The scene was once very spectacular. Have you ever wondered why a good road is congested?

Many drivers have encountered such a strange thing: they were driving and suddenly got stuck in a traffic jam. They moved forward little by little, but found that there was no accident in front of them, and there were no other special conditions. It was incredible. What is the reason for this phenomenon called " ghost traffic jam " by the traffic police? Have you encountered it?

Sudden braking + random lane changes = "ghost traffic jam"

The so-called "ghost traffic jam" means that when there are many cars on the highway, as long as there is any slight disturbance, such as a driver changing lanes, briefly braking, or even just slowing down a little because of distraction, the cars behind will slow down, and then it will trigger a series of pauses, forming a virtual traffic jam.

This traffic jam will cause more and more vehicles to pile up, gradually spreading to the far rear, causing serious traffic jams. Studies have shown that on a highway with a lot of vehicles, a novice driver's sudden braking may affect a section of road as long as 80 kilometers.

Nagoya University in Japan once conducted an experiment to explain this phenomenon. Many cars were allowed to travel at a constant speed in a circle. According to this logic, traffic jams should not occur. However, as time went on, some cars inexplicably got closer to the car in front, and as they got closer and closer, they had to step on the brakes. As the impact grew, a traffic jam occurred!

Phantom traffic jam experiment

A cat suddenly crossed the road

There will be a chain reaction

Traffic lights are equivalent to adding a disturbance to normally moving vehicles. Every time the light comes on, the driver's reaction time is different. It is very likely that when a large stream of vehicles passes the green light and it happens to be your turn, the green light turns red (I believe you have experienced this, please describe your feelings).

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Even in places without traffic lights, if a cat suddenly crosses the road, it will cause a series of reactions. Even if the cat has left, the impact cannot be eliminated immediately, as if the vehicle has passed through an invisible intersection.

Therefore, traffic jams often occur at bottlenecks, such as narrowing roads, reduced lanes, traffic accidents, intersections, etc. In these places, once someone steps on the brakes, it will cause a series of chain reactions.

Even if the driver can stay absolutely focused, he will still frequently encounter various intersections or various strange emergencies, such as the cat mentioned above. Road traffic is a complex multi-body system, and any disturbance will destroy its balance and cause traffic congestion. There are no intersections on the highway precisely to avoid this.

Therefore, when driving, you should pay attention to maintaining an appropriate distance from the vehicles in front and behind you . In this way, when the car in front brakes, you have enough reaction distance and do not need to brake too hard. The same goes for the car behind you. This can shorten the time when the traffic flow shrinks and return to normal driving state in a shorter time.

How to solve the "ghost traffic jam" problem?

"When driving on the road, we are not afraid of slowness, but standing still." Traffic police summarized the hidden dangers that affect the smooth flow of traffic, including sudden stops and turns, random lane changes, forced cutting in and overtaking, random parking, and interference between motor vehicles and non-motor vehicles. If we can maintain a relatively uniform speed, observe in advance when entering and exiting intersections, and give way when necessary, we can avoid similar "ghost traffic jams".

Mathematicians at MIT have tried to find a solution to the "phantom traffic jam" problem through mathematical model analysis. The mathematical model shows that if drivers reduce their speed and drive at a fixed speed instead of stopping and driving suddenly, they can not only save fuel, but also have the hope of eliminating the "phantom traffic jam" phenomenon.

Planning and production

Source: People's Daily

Editor: Yang Yaping

Proofread by Xu Lailinlin