Traffic quality
The traffic quality is a mathematical variable that has to be determined when planning roads . With the calculation of the traffic quality it can be proven that the new road can handle the expected traffic load with a desired quality and that the given travel speed according to RAS-N is reached. Proof of traffic quality can only be calculated on two-lane country roads outside intersections and for roads in category groups AI to A III.
Input values
The following input values are required to prove the traffic quality:
Cruising speed V B
This speed is an average value for all cars that is aimed for on the new road section. It is specified by the regional planning and regional planning.
Rated traffic volume q B
This value reflects the traffic demand (including heavy traffic share b SV ) on the new route section. It can be determined from the traffic forecast . You can refer to a traffic report ( model forecast ) or an extrapolation ( trend forecast ).
Lines of the route in position and height
This information is required in order to take the gradient and curvature into account when verifying the traffic quality.
Divide the road into equal sections
The road should be divided into equal sections. The division is particularly dependent on the longitudinal slope and curvature. The route sections should not be smaller than 300 m.
calculation
Assign input values for calculation
The route sections are assigned gradient classes (1 to 5). Depending on the longitudinal slope, the fictitious assessment vehicle reaches a different mean speed. In addition to the gradient class, the curvature and the proportion of heavy traffic are determined for each route section. These variables have a significant influence on the traffic quality.
Traffic volume
The traffic volume within the route sections can be determined from the above values using tables. It has the unit of motor vehicles per hour and relates to both lanes .
Traffic density
In order to determine the traffic quality, a ratio of traffic volume and average car travel speed must be formed. Based on this fictitious traffic density, measured in vehicles per kilometer, the new road can be divided into quality levels.
see also main article traffic density
Result
Level of service quality
Depending on the traffic density, the road can have quality level A (good traffic quality) to level F (poor traffic quality). If the desired quality level from the planning specification is not achieved, measures must be taken to produce the required quality.
The definition of the quality levels is u. a. published in the manual for the dimensioning of road traffic systems (HBS) of the FGSV .
- Level a
- Road users are very rarely influenced by others. You have the desired freedom of movement to the extent that it is permitted on the traffic system. The flow of traffic is free.
- Level B.
- The presence of other road users is noticeable, but causes only minor impairment of the individual. The flow of traffic is almost free.
- Level C
- The individual freedom of movement often depends on the behavior of the other road users. The freedom of movement is noticeably restricted. The traffic condition is stable.
- Level D
- The traffic flow is characterized by high loads, which lead to significant impairments in the freedom of movement of road users. Interactions between them take place almost constantly. The traffic condition is still stable.
- Level E.
- There are constant mutual hindrances between road users. Freedom of movement is only given to a very limited extent. Slight deterioration in the influencing variables can lead to the collapse of the traffic flow. Traffic moves in the area between stability and instability. The capacity is reached.
- Level F
- The demand is greater than the capacity. The traffic system is overloaded.
See also
literature
- Natzschka: road construction, design and construction technology . BG Teubner Verlag, 1996, ISBN 3-519-05256-3
- Wendehorst: Structural number tables . Teubner-Verlag, 31st edition ISBN 3-519-55002-4