Evenness of the longitudinal profile/longitudinal evenness: According to the Road and Transportation Research Association's technical test regulations for measuring evenness of roadway surfaces, a road's evenness is a surface property of relevance to users, and among the attributes determining utility value as well as intrinsic value.
The following factors can be derived specifically from evenness:
- Safety and comfort for road users
- Noise pollution levels
- Risk posed by splashing water
- General road condition
- Bookkeeping value for the operator
A road's evenness is determined by measuring the longitudinal evenness (sub-project 1a [TP1a] of ZEB; longitudinal alignment with respect to the direction of travel) and transverse evenness (sub-project 1b [TP 1b] of ZEB; transverse alignment with respect to the direction of travel). These evenness parameters can be determined by means of "contact measurements", e.g. using a straightedge, or "contactless measurements" with the aid of sensors on a measuring vehicle. Contactless measurements by comparison offer significant advantages such as those listed next:
- Data is collected much more quickly, accurately and objectively
- Considerably longer wavelengths are registered for longitudinal evenness (up to 50 m are prescribed by ZTV-ZEB-StB1)
- Values are measured continuously and not just sporadically
- The high-speed vehicles used here eliminate the need for road blocks
To be able to quantify longitudinal evenness, the recorded values (see the schematic representation) are used to calculate elements such as the degree of unevenness (AUN), ripple (W), effective longitudinal evenness index (LWI) and international roughness index (IRI) in accordance with the provisions of the FGSV. These figures are then incorporated, together with other variables such as those determined during measurements of transverse evenness and traction, via a defined weighting pattern into the overall assessment of road condition.
The multifunctional measurement systems ARGUS® and ARGUS®-PROFI are used to record measured values (raw data). Special measuring methods based on the principle depicted above allow highly accurate, speed-independent measurements of high repeatability. The data thus acquired serve as a reliable basis for subsequent calculation of key figures enabling transparent prioritization of measures to improve longitudinal evenness.
Capabilities of the ARGUS® system in terms of measuring longitudinal evenness:
- Registration of longitudinal uneveness in the wavelength range from 0.2 to 100 m through multiple scanning with 4 laser distance sensors
- Online monitoring and pre-processing of measured values by the vehicle's computer
- Output of the highway’s actual longitudinal altitude profile (measured in the right-hand track) with a horizontal resolution of 10 cm and vertical resolution of 0.025 mm
- Calculation of elements such as AUN (general unevenness), ripple and IRI (international roughness index)