Design consistency is becoming an essential component of highway design. The most frequently used criteria to evaluate design consistency are the difference between design and operating speed, operating speeds on successive elements and assumed side friction of the road and the side friction demanded by the driver. For design consistency analyses on new alignments it may not be possible to use actual operating speed data as the new alignment may be too different, thus speed prediction models can be used to estimate operating speed. Estimates of operating speed can influence the outcome of design consistency criteria calculations. Therefore, it is important to understand how design consistency measures are influenced by the selection of operating speed models. There has been a considerable research effort devoted to the data collection for and derivation of speed prediction models for horizontal curves and to a lesser extent tangent sections. Similarly, there has been considerable effort in developing design consistency measures and evaluation tools. However, little research has been done into the influence that different speed prediction models have on design consistency criteria. This paper investigates how the selection of speed prediction models influences design consistency evaluation. The research found that the selection of the speed prediction model has a significant impact on design consistency evaluation.
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