Effect of Pavement Roughness on Speed of Vehicles

The surface condition of pavement influences traffic safety, operating speed, manoeuverability, driver comfort and service volume. Generally, the service quality provided by pavement surface is evaluated based on its roughness. International Roughness Index (IRI) is a roughness indicator used globally. Even though the measurement of IRI is very costly, it gives a standardised method of pavement unevenness evaluation. This study attempts to relate pavement roughness with the speed of different classes of vehicles. Pavement roughness and traffic flow characteristics were collected from thirteen sites in Calicut city. Traffic data was collected using a Transportable Infrared Traffic logger (TIRTL), while geometric data was collected manually. Surface roughness was measured using the Machine for Evaluating Roughness Using Low-cost Instrumentation (MERLIN), and the Cundill roughness equation was used for IRI calculation. As IRI increases, the Free-Flow Speed (FFS) and Peak Hour Speed (PHS) of different vehicle classes reduce. The reduction in FFS is linear with IRI, whereas a negative logarithmic relationship can be observed in the case of PHS.