Abstract:
Crash rates are said to be nearly three times higher on curved sections than those on
straight sections of rural roadways. As a result, advisory curve/speed signs are standard
practice to mitigate these risks on sharp horizontal curves. The industry standard for
determining appropriate and uniform speeds for such signs has long been the ball-bank
indicator; however, debates over suitable ball-bank thresholds continue and inconsistent
standards between jurisdictions persist. Moreover, research regarding the effectiveness
of advisory speed/curve signs in general has been long neglected. This project focuses on
current posting procedures in Oregon, methods that can be used to evaluate advisory
speed posting techniques, and their impact on users with respect to increased system
safety. This evaluation of current procedures reveals the impact of changing current
Oregon policy to conform to proposed changes in the Manual of Uniform Traffic Control
Devices and the Traffic Control Device (TCD) Handbook. Additionally, the comparison
of a limited set of curves suggests that advisory curve/speed signs may effectively reduce
the number of crashes at horizontal curves. This study targets rural roadways in Oregon,
and has data randomly sampled from 166 state and county maintained facilities to support
the analysis (with a total of 232 curves). This report is intended as a call-to-action for the
research community, and provides areas that future studies should investigate.
