Functional assessment of longitudinal road evenness by the weighted longitudinal profile (WLP)

Abstract

Longitudinal evenness is one of the most important quality criteria of roads. Vehicles can be regarded as dynamic systems consisting of masses, springs, hydraulic dampers, anti-roll bar etc. They are governed by mechanical laws, i.e. when passing the road, the systems respond to the unevenness with vertical excitation. The impacts are multifaceted. In addition to effects on road safety, driving comfort and pavement loading, the dynamic forces enhance the vehicle’s resistance to movement and consequently the vehicle’s energy demand. This in turn leads to a higher energy consumption and subsequently to an increase in CO2 emissions in road traffic. Against this background, the quality criteria for longitudinal evenness need to be defined by the mechanical impact on drivers and road construction in order to meet the concerns of road users and public authorities. For the assessment of longitudinal evenness, several indicators are in practice. In many countries, the IRI (International Roughness Index) is used for assessment purposes as well as for acceptance of construction works. However, the IRI depends on the velocity and, strictly speaking, on the mechanical system it represents. In order to overcome these shortcomings, the WLP (Weighted Longitudinal Profile) has been developed. Irregular, periodic and transient manifestations of unevenness can be individually addressed, safely detected and precisely located. It takes into account the entire range of speeds and dynamic properties relevant to road traffic. The paper covers the explanation of the indicator, the relationship to vertical dynamics, the deduction of limiting values and the application to road evenness data. The results are visualized and compared to the conventional approach.