Berhanu, Girma(PhD)Mekonnen, Behailu2018-06-182023-11-112018-06-182023-11-112007-02http://etd.aau.edu.et/handle/12345678/1341Design consistency is the conformance of highway’s geometric and operational features with driver’s expectancy. A technique to evaluate the consistency of a design is to evaluate changes in operating speeds along an alignment. To use operating speed as a consistency tool requires the ability to accurately predict speeds as a function of the roadway geometry. The current Ethiopian Roads Authority geometric design manual is based on the design speed concept. However, due to the constraints resulting from roadway elements, right-of-way, and environmental features, consistency in operating speed cannot be guaranteed. In order to make informed decisions to ensure highway geometric design consistency, the consistency of geometric design of operating speed on simple curve and tangent section was studied. Forty three sections for both of horizontal curve sections and tangent sections were selected, within easy reach of Addis Ababa. Roadway geometric design variables were obtained from design documents and through field measurements. The speeds of passenger cars, buses, and trucks were measured on each curve and its approaching tangent, under dry day time condition. This study was focused on two major issues, in evaluating the geometric design consistency of the selected alignments and in developing operating speed predicting models for the selected sections. Therefore, the results obtained from consistency evaluation shows that four sections between simple curves and tangents were in poor conditions. Whereas, consistency evaluation between design speed and operating speed shows that thirty seven sections in horizontal curves and thirty four sections in tangents sections was in a poor conditions. Two models were found for horizontal curves and tangents. Model found for the horizontal curves were governed by the combination of grade and superelevation. Furthermore model for tangent section were governed by grade.enTrunk RoadsThesis