The more than 617,000 bridges across the United States carry 176 million trips daily, according to the ASCE 2021 Report Card for America’s Infrastructure. Inspections are essential to ensure that these structures are safe. But it is not just the bridge structure that needs to be inspected; the approach slabs to bridges are also of concern. The approach slab, the area where the roadway connects with the bridge abutment, can experience compaction and settlement, affecting the smooth transition for vehicles. Possible bumps at the bridge approach can affect vehicles as well as the structural reliability of the bridge due to the increase in vehicles’ dynamic load. The best way to address this is to regularly inspect bridge approach slabs.

In this study, researchers Guolong Wang, Kelvin C.P. Wang, Guangwei Yang, Joshua Qiang Li, and Walt Peters, used a new generation of high-speed 3D laser imaging to evaluate the roughness of bridge approach and departure slabs. Using the international roughness index the authors evaluated 98 bridges of varying lengths and a mix of approach slabs using asphalt concrete pavements and portland cement concrete pavements. Two- and three-dimensional images were leveraged for surface distress analysis on the bridge approach and departure slabs and bridge deck joints. The researchers’ paper “Evaluation of Bridge Approach Slab and Dynamic Load Allowance Using Sub-mm 3D Laser Imaging Technology” in the Journal of Bridge Engineering, demonstrates that 3D imaging systems can be an important data source to provide comprehensive nondestructive data without traffic control. Learn more about how this research can assist engineers to evaluate bumps more effectively in bridge approach and departure slabs at The abstract is below.


Current evaluation of bumps at bridge approaches is limited in scope and performance, and varies in practice at different state DOTs. This study intends to propose a general criterion specifically for bridge approach bump classification and develop a formula for dynamic load allowance (IM) estimation for bridges in Oklahoma. A total of 98 bridges in Oklahoma were studied using recently developed sub-mm 3D laser imaging technology that simultaneously collected inertial profiles, sub-mm 2D/3D images, and right-of-way images at highway speeds for roughness and distress analysis. A three-level criterion that evaluates maximum roughness within an approach or departure slab is established to classify approach bumps into Good, Fair, and Poor conditions. The threshold defined in the criterion considers both the field crew’s sensation during data collection and the surface distresses that cause or are associated with different levels of International Roughness Index magnitudes. The development of the formula for bridge IM estimation is based on the established criteria while incorporating the influences of bumps from approach slab and bridge deck. The results of evaluating approach bump and IM of 98 bridges demonstrate the ability of using sub-mm 3D laser imaging technology to evaluate bridge approach bumps and bridge IM in an efficient and effective manner.

Discover more about how to use 3D laser imaging to assess bridge slab distress in the ASCE Library: