# Traffic flow

The traffic flow is defined in traffic planning as the number of changes in location between two points during a certain period of time. Starting from the source , it leads to the destination and is therefore depicted with the symbol . ${\ displaystyle i}$${\ displaystyle j}$${\ displaystyle v_ {ij}}$

Both the traffic volume and the traffic density can be calculated from the number of individual elements in a traffic flow .

## species

If the traffic flow relates to a certain area (for example a traffic cell in a planning or investigation area), the following types of traffic flow can be distinguished with regard to the direction of the flowing traffic:

 Target traffic or irradiating traffic includes changes in location that begin outside and end in the area under consideration. Source traffic or broadcast traffic includes changes in location that begin in the area under consideration and end outside of it. External traffic includes changes of location that take place between sources and destinations outside the area under consideration. Through traffic (through traffic) includes changes of location that pass through the area under consideration and begin and end outside. Broken through traffic includes changes of location that begin and end outside and lead through the considered area with a small subordinate stop. Returning target traffic is a sequence of changes in location, the first change of location of which ends in the area under consideration and the last change of location leads back to the starting point of the first change of location. Returning source traffic is a sequence of changes in location whose first change of location begins in the area under consideration and whose last change of location leads back to the starting point of the first change of location. Inland traffic includes changes of location that only take place within the considered area. Adjoining owner / riparian / Anstösserverkehr including target source and domestic traffic and broken through traffic, so all traffic without the outer and the pure transit traffic in the narrow sense ( riparian relates both to the actors as the traffic destination)

## use

### Structural aspects

Current load plan of an intersection

Within road traffic junctions, there are traffic flows for all driving relationships used (crossing process). A normal four-armed intersection knows a total of twelve different vehicle traffic flows: from north straight to south, from north turning right to west, from north turning left to east, from west straight to east and so on.

Traffic relationships used by pedestrians are also referred to as traffic flows. If there is a pedestrian ford over each of the arms at a four-armed intersection, one speaks of a total of eight pedestrian traffic flows; a distinction is made according to the direction of walking. The same applies to signaled cyclists or public transport that are separated from other traffic.

A traffic flow that has to pay attention to a signal is called "signaled traffic flow". A signaled traffic flow is called "clearing" in the first few seconds after the end of its clearance time , while it is called "moving in" when its clearance time has just started.

Traffic flows that turn left or right are referred to as “turn flows”. Priority traffic flows are referred to as main flows, traffic flows requiring waiting as secondary flow.

### Traffic management and control engineering

For traffic-dependent control procedures of road traffic junctions, the traffic flow is used to "map an observable class of road users". If, for example, buses can be detected independently of the other traffic (with special bus detectors), buses can form their own traffic flow even though they use the same lane as the other traffic. This separation enables the control method to treat buses at the signal with a higher priority ( local public transport priority ) than the rest of the traffic, even if there is no special signal for the buses.

VS-PLUS is an example of such a control procedure .

### Traffic planning

In traffic demand models, traffic flows are referred to as the source-destination relationships between the traffic cells, for example a place, a region or just a residential area. For example, the ratio of through traffic to local traffic decides whether a bypass would be appropriate for the former.

Traffic flows can u. a. can be mapped in traffic flow matrices.