Posting advisory speed signs at sharp horizontal curve sites is a practice well established in the United States. The purpose of these signs is to provide the driving public with a safe speed to negotiate such curves; however, the link between these signs and safety has not yet been clearly established.
The first manuscript in this dissertation presents an effort to model safety as it relates to curve advisory speed signs. It proposes a statistical model relating crash frequency at 2-lane rural highways in Oregon to curve advisory speed signs and other influential factors. The Advisory Speed Crash Factor (ASCF) emerges as a sub-model that characterizes the safety effect of advisory speed signs. Results indicate that safety may be compromised if the advisory speed is either excessively prohibitive or excessively permissive.
The second manuscript extends the use of the proposed ASCF to develop the OSU posting method, a new procedure that procures the "optimal" advisory speed derived from the ASCF. A field validation analysis, also presented in this manuscript, verified the meaningfulness of the proposed ASCF sub-model.
The third manuscript outlines another methodology, named 'the Hybrid OSU Posting Method' in an effort to mitigate the well documented variability associated with using the Ball Bank Indicator (BBI). This method determines the advisory speed using the BBI in combination with the ASCF. Though benefits in safety performance and consistency resulted from using the Hybrid OSU method, this method is still outperformed by the computational OSU method.