Traffic flow
Under traffic flow refers to the flow or flux, d. H. the number of traffic elements (e.g. vehicles ) that cross a certain traffic area or line (as a borderline case of the area) per unit of time .
Changing the flow of traffic with certain boundary conditions - traffic or vehicle density , average speed of one or all vehicles, speed distribution, safety distance , street width - is a complex research area, since many phenomena can only be described non-linearly . Traffic simulations - in German-speaking countries for example VISSIM - are therefore an important tool to support the analytical models. In particular, the conditions for the transition from unhindered flow to stop-and-go traffic or traffic jams are of interest. Research results are used in so-called telematics .
Traffic flow analysis
Traffic flow analyzes can take place on different scales:
- microscopic level
- Each vehicle is considered separately and an equation for describing its speed, usually a differential equation, is established for each vehicle .
- macroscopic
- By analogy with models from fluid dynamics , it is often more useful to set up a system of partial differential equations for summary phenomena such as vehicle density or average speed. For example, the traffic equation establishes a connection between the change in traffic flow over time and the local change in traffic density.
- mesoscopic (kinetic)
- A middle way is the definition of a function f (t, x, V) which indicates the probability of occurrence of a vehicle at time t at location x with a speed V. This function can be calculated using methods of statistical mechanics such as the Boltzmann equation.
Traffic flow in different traffic systems
Road traffic
In road traffic , the term describes the use of the traffic routes by "moving" traffic. This means that the flow of traffic initially increases with higher speed , but can also decrease again due to the disproportionately increasing distances or greater speed differences and the associated mutual obstructions.
Basic concepts of traffic flow in road traffic:
- The flow of traffic can generally be described as vehicle flow . These are vehicles traveling in the same direction on a lane .
- If there are two or more vehicles behind one another on a lane , they form a row of vehicles . There is no mutual influencing of the individual vehicles in a vehicle row.
- If a vehicle in front of a row of vehicles influences the speed of the following vehicles, a column of vehicles (also known as a vehicle crowd) is created. The vehicles following the vehicle in front form a queue of vehicles .
Influencing variables for the optimization of the traffic flow are:
- Behavior of the individual driver , for example by accelerating when starting a traffic light and cooperative driving style.
- Influencing the ongoing traffic through traffic control systems, for example by regulating the maximum permitted speed or approved lanes via electronically controlled display boards . In cities, on the other hand, the challenge for traffic management is to set up the correct cycle times for the traffic lights .
- Systematic phenomena - when, for example, a traffic jam arises out of nowhere at a certain traffic density , as described in the Nagel-Schreckenberg model .
- Traffic planning , which has to set up and maintain the traffic infrastructure according to requirements, whereby aspects of environmental protection are also taken into account.
Measures to optimize the flow of traffic are:
- Speed signal and green wave
- Reduction of the conflicting traffic directions in a traffic node .
- Multi-lane expansion
Rail transport
In rail traffic , the term describes the use of the traffic routes by "moving" traffic. This means that the flow of traffic initially increases with higher speed , but can also decrease again due to the disproportionately increasing distances or greater speed differences and the associated mutual obstructions.
Influencing variables for the optimization of the traffic flow are:
- Modern line train control and high-speed train units combined with better routing on high- speed lines with the omission of terminal stations .
- Extension of the time window in the traffic hubs in the metropolitan areas .
- Skilful time management , carrying out renovation and repair work in times of low traffic and suspending the track construction work at peak times .
- Use of additional wagons and special trains on special occasions.
Shipping
In shipping , the term describes the use of the traffic routes by moving traffic. This means that the flow of traffic initially increases with higher speed , but can also decrease again due to the disproportionately increasing distances or greater speed differences and the associated mutual obstructions.
Influencing variables for the optimization of the traffic flow are:
- Block handling at movable bridges and locks (inland traffic)
- Expansion of natural waterways to achieve constant depth (inland traffic)
- GPS and nautical systems to ensure higher vehicle throughput (inland traffic)
- Widening the port entrances and improving the fairway (sea traffic)
air traffic
The concept of traffic flow also exists in air traffic, although an aircraft uses assigned air corridors and other altitudes in flight . This therefore refers only to the ground handling , the rolling process , at the start and landing and that precise time frame must be adhered to.
See also
- Three-phase traffic theory
- Fundamental diagram of traffic flow
- PELOPS (traffic flow simulation program)
- Traffic speed
- Traffic physics
literature
- Alex Erath, Philipp Fröhlich: The speeds in car traffic and the capabilities of roads over the period 1950–2000 . In: IVT, ETH Zurich (Hrsg.): COST 340: Development of the transit traffic system and its impact on the use of space in Switzerland . Work Report 183 Traffic and Spatial Planning, February 2004 ( ivt.ethz.ch [PDF]).
Web links
- Traffic flow and speed. In: Mediathek. Bielefeld Transport Institute V., accessed on September 22, 2009 .