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.
