The evaluation of change s in operating speeds along the alignment is effective in checking the consistency of the road because it can identify the horizontal curves that require an excessive speed reduction in respect of the approaching speed to be traveled safely. However, to use the operating speed-profile as a consistency tool it is necessary to accurately predict the speed as a function of the road geometry. Therefore, an operating speed-profile prediction model was developed specifically for the Italian two-lane roads using data collected on tangents and curves representative of the common condition found in Italy. The model includes prediction equations for desired speed on long tangents, operating speed on curves, acceleration and deceleration rates. The model takes into consideration the general character of the horizontal alignment, through the use of the curvature change rate of the road, to estimate the desired speed and to improve the accuracy of the speed prediction on curves. The operating speed-profile model proposed is an effective tool for the evaluation of design consistency and for other safety analyses of new and existing road.
