This paper was presented at the "Speed limits, safety and special conditions" session. These proceedings are available on CD-ROM. Curves that do not meet the minimal design standards exist on our road systems. To warn drivers of the presence of such curves, many road authorities choose to do so by recommending a safe speed. In Quebec, when a curve's safe speed is found to be more than 10 km/h below the road's speed limit, the curve is identified as `substandard', and is signed with the appropriate road signs and delineation. Thus, the substandard curve is signed with a curve warning sign supplemented by an advisory speed plate. However, despite the presence of the advisory speed signs, it seems that more and more drivers exceed these speeds without being in any apparent danger. Furthermore, the recommended speed reduction does not always reflect the same level of danger. In 1993, a research project was initiated to verify these impressions. The main objective was to review the existing methodologies to determine safe and advisory speeds in order to develop and recommend a method that would meet both the road authority's and the driver's expectations. The project now completed, the results of our study show that the methods available to determine safe speeds have their weaknesses. It is the lack of consistency with which the advisory speeds are posted, though, that explains a part of the loss of credibility they have undergone. A new method, similar to the traditional ones, is also presented. (A)
Abstract