Investigation of Pavement Distresses Condition and Its Influence on Macro Traffic Parameters: A Case of Harar to Dhangago Road Segment.

Abstract

Pavements are designed for desired speed limits and traffic capacity over time without considering the effects of more distinct pavement distresses parameters. However, various forms of pavement characteristics, causes an impact on the traffic stream, particularly free-flow speed, roadway capacity and density. The target of this research was to identify the distresses condition and its influence on macro traffic parameters such as speed, capacity and density of the road segment along Harar to Dhangago segment. In order to achieve the objective of this research, the necessary data were collected at the study site. The data collection process included field visual inspection, field measurements and traffic data video recording. Typical data required for the assessment of pavement impact on traffic flow were processed and analyzed based on directempirical method. The observed traffic volumes and speeds were used to derive densities- flow equation. In addition, the least square regression method was used for estimation of the model coefficients. The results of the research showed that the PCI value ranges from 10 to 84, which indicated a section of the road had all most all types of pavement condition Rating. From the pavement condition survey analysis, it was identified that; good, fair, poor, and serious covers equal 20% in each case, While, the remaining percent is covered by Very poor and failed section. Based on the pavement condition rating, traffic data for four study sections, a section rated ‘good’, free flow speed estimated of about 73.37km/hr, and the optimum speed is 37km/hr. However, once the pavement distress impact is factored in, optimum speed dropped to 29.6km/hr in ‘poor’ section. As pavement condition rated ‘very poor’, the analysis indicated that the impact of distress on optimum speed reduced by 34.23% when compared to the section rated ‘Good’, dropped to 24.33km/hr. On the other hand, the Optimum speed of ‘serious’ section reduced by 52% when compared to the section rated ‘Good’. It is therefore concluded that there is a strong influence of pavement distresses condition on the traffic flow parameters. Hence, for varying PCI and PCR values, the road sections rated ‘Good’, it is recommended to provide crack sealing and minor patching. Likewise, for sections rated ‘Fair’, seal coating or thin nonstructural overlay of 50mm or more, is one of the best options to restore as-is service condition of the pavement. While sections rated ‘Poor’ and failed sections, should have to be corrected by in-depth patching and repair with major overlay and reconstruction with an extensive base repair, respectively.