Development of a Bridge Smoothness Specification for Illinois DOT

Smoothness is considered to be the most important ride quality by the highway user. Although bridges are much rougher than pavements, most of the studies conducted to improve pavement smoothness have been focused solely on pavements. This report describes the effort of the University of Illinois to develop a preliminary bridge smoothness specification for the Illinois Department of Transportation (IDOT). The preliminary specification presented in this research report is based on the testing and analysis conducted under this study and reflects the views and experience of the authors. It is emphasized that this draft specification is not intended for use in construction without significant additional development and field testing. The most suitable index and equipment are recommended based on a literature review of smoothness indices and different pieces of equipment. In addition, International Roughness Index (IRI) and Profile Index (PI) values were computed from testing 20 recently constructed or rehabilitated IDOT bridges in Illinois using a lightweight profilometer. These data were analyzed in order to set up smoothness limits for bridges, and a correlation between IRI and PI was established.