According to the FGSV's technical test regulations for evenness measurements on highway surfaces, road evenness is a user-relevant surface property, and among the attributes which determine 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 condition of the road
- 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 are collected much more quickly, accurately and objectively
- Considerably longer wavelengths are registered for longitudinal evenness (up to 50 m are prescribed by ZTV-ZEB-StB)
- 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 transverse evenness, the measured values (see the schematic representation) are used to calculate, in accordance with the provisions of the FGSV, parameters such as rut depth and fictitious water depth as measures of the potential risk of aquaplaning. The transverse inclination of the vehicle/measuring beam is also recorded. These figures, together with other variables such as those determined during measurements of longitudinal evenness and traction via a defined weighting pattern are then incorporated into the overall assessment of road condition.
The multifunctional measurement system ARGUS® is 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 serves as a reliable basis for subsequent calculation of key figures enabling transparent prioritization of measures to improve transverse evenness.
Capabilities of the ARGUS®- system in terms of measuring transverse evenness:
- Scanning of the road surface with, depending on lane width, up to 37 laser distance sensors mounted on a cross member at lateral measurement intervals of 10 cm
- Continuous recording of the transverse profile over the entire lane width
- 50,000 scans per second at a resolution of 0.025 mm
- Collection of raw data for subsequent calculation of elements such as internal rut depth, fictitious water depth, transverse inclination and, as required, additional transverse evenness indicators and statistics