Riding quality affects the vehicle speed, which finally impacts on the cost of travel time for road users. International Roughness Index (IRI) is commonly used to describe road roughness. In previous studies, scholars used simulation models to make regression analysis of IRI and traveling speed. However, the simulation models can not reflect the actual traffic conditions, and the experiment sample sizes in most studies are small. This paper analyzes the relationship between IRI and free-flow speed through the measured IRI data and traffic data of Shanghai Urban Expressway in three years. The results show that there is a significant linear relationship between IRI change and free-flow speed change. For sections with different lanes, the relationship is different. When the IRI is increased by 2 m/km, the free-flow speed of 2-lane section is reduced by 3.2 km/h, and the 3-lane section is reduced by 1.6 km/h.

CICTP