Potential Bias of Response Type Road Roughness Measuring Systems: Causes and Remedial Measures

Response-type road roughness measuring systems are widely used for collecting roughness data of pavement in many countries. These systems estimate IRI from correlation equations of IRI with other variables and help collect roughness data in a short time comparing to many Class I and Class II devices. Although they produce roughness data rapidly, most of them still have the restrictions in survey speed. It is recommended to maintain the survey speed within a certain range or at constant speed. But maintaining the speed within a certain range is quite difficult due to the existence of traffic control devices and the friction with other vehicles. Therefore, these systems can produce a significant bias in roughness measurement if the survey speed is not properly maintained. The objective of this study is to develop a calibration equation that eliminates the bias produced by speed constraints and allows any survey speed. A simplified procedure that produces a regression relationship for IRI with bump integrator reading and survey speed as explanatory variables is developed using ROMDAS bump integrator. Moreover, this study investigates how the bias created by speed fluctuation affects the outcome and demonstrates how alternative method eliminates that bias using a case study