Operating speed is one of the best performance measures that can tell transportation agencies how well or how poorly the transportation system is functioning. Fluctuating operating speeds often mean there is a design flaw or something about the physical road design that violates drivers' expectations. A primary example of this is a horizontal curve on a highway that had a reduced recommended advisory speed. Traditionally, researchers and transportation agencies measure operating speeds along the approach tangent to a horizontal curve and at the midpoint of the curve. This thesis looks at the significance of alternate measuring locations within the curve. It also analyzes the difference between the 85th percentile maximum speed reduction and the more traditional measure of the reduction in 85th percentile speeds, which is used as an indicator of safety. / Graduation date: 2012