Design consistency is the conformance of highwayâ€™s geometric andrnoperational features with driverâ€™s expectancy. A technique to evaluate thernconsistency of a design is to evaluate changes in operating speeds along anrnalignment. To use operating speed as a consistency tool requires the abilityrnto accurately predict speeds as a function of the roadway geometry. Therncurrent Ethiopian Roads Authority geometric design manual is based on therndesign speed concept. However, due to the constraints resulting fromrnroadway elements, right-of-way, and environmental features, consistency inrnoperating speed cannot be guaranteed. In order to make informed decisionsrnto ensure highway geometric design consistency, the consistency ofrngeometric design of operating speed on simple curve and tangent section wasrnstudied. Forty three sections for both of horizontal curve sections andrntangent sections were selected, within easy reach of Addis Ababa. Roadwayrngeometric design variables were obtained from design documents andrnthrough field measurements. The speeds of passenger cars, buses, andrntrucks were measured on each curve and its approaching tangent, under dryrnday time condition. This study was focused on two major issues, inrnevaluating the geometric design consistency of the selected alignments andrnin developing operating speed predicting models for the selected sections.rnTherefore, the results obtained from consistency evaluation shows that fourrnsections between simple curves and tangents were in poor conditions.rnWhereas, consistency evaluation between design speed and operating speedrnshows that thirty seven sections in horizontal curves and thirty four sectionsrnin tangents sections was in a poor conditions. Two models were found forrnhorizontal curves and tangents. Model found for the horizontal curves wererngoverned by the combination of grade and superelevation. Furthermorernmodel for tangent section were governed by grade.