Jam out of nowhere
A traffic jam that arises without an objective blockade or overloading of the traffic route is called a traffic jam out of nowhere (also called phantom traffic jam ) .
Emergence
A traffic jam arises out of nowhere when vehicles behind in a column have to brake harder than the vehicles ahead in order to avoid rear-end collisions. Possible reasons for this are insufficient safety distance, significant differences in speed or the location of the end of a traffic jam behind a blind spot (curve, hilltop). The excessive braking increases from vehicle to vehicle until a first vehicle comes to a standstill and the following inevitably also - a traffic jam emerges out of nowhere.
On the front (unobstructed) side of the traffic jam in the direction of travel, each vehicle needs one to two seconds to accelerate again from a standstill and clear a road length of 5 to 10 meters for the following vehicle to start up. The front of the traffic jam therefore moves against the direction of travel at a speed of around 15 km / h. It only comes to a standstill when it comes to an area with so little traffic that it is no longer necessary to brake hard.
Scientific investigations
The process of non-compliance with the safety distance, excessive braking, short-term fluctuations in speed or delayed acceleration is described by the Nagel-Schreckenberg model .
When traffic is low, traffic jams remain localized out of nowhere and quickly dissolve. With a larger number of vehicles per route section, the individual traffic obstructions are related to each other and combine to form longer traffic jams.
The investigation by the University of Cologne revealed four causes:
- Driving too close, which can cause the first and all following cars to brake suddenly,
- Unlocking too quickly and therefore slowing down just as quickly and
- mentally under-challenged to keep a sufficient distance in slow-moving traffic, because the drivers wander with their thoughts.
- counterproductive driving in order to move faster on the lane with supposedly more flowing traffic ( jumping in columns ).
The drivers who cause the traffic jam at the beginning do not experience the consequences of their behavior, because the traffic jam only begins far behind the cause and moves against the direction of travel. The person causing the traffic jam does not receive any immediate feedback and cannot question his behavior.
"Nothing"
Colloquially, “nothing” in connection with the “traffic jam out of nowhere” usually means the absence of an accident, a traffic density tending to become congested, or a “disruption” or a “bottleneck”, e.g. B. understood a motorway entrance. However, for a long time it was unclear whether minor causes, such as increased lane change frequency, are necessary or whether a traffic jam can arise even without this. Violations of the right-hand drive law as well as curious road users when vehicles break down (breakdown) or accidents in the opposite direction also play a role here. In an experiment in Japan (see web links), among other things, it was possible to show that congestion waves occur from a certain traffic density even if the driver is explicitly asked to drive steadily. Even if this is the aim, the human driver lacks the ability to implement this desired, uniform driving behavior. For the future, there is hope that with the given traffic density, traffic jams can be avoided by driver assistance systems compared to today, or that the traffic density can be increased by driver assistance systems with the same frequency of traffic jams and the same journey times.