An index for sight-hidden dips assessment

This paper presents a practical procedure using a completely new index to determine whether a sight-hidden dip (SHD), a common shortcoming in vertical alignment, is critical for traffic safety. This sort of hidden section could be a hazard for drivers since head-on crashes may occur during passing manoeuvres. Software which estimates sight distance and is based on geographic information systems was utilised to assess real cases of SHDs, according to the German guidelines for visualisation of highways. Also, a previously existing analytical method was used to perform the same analysis and the results were compared. Moreover, the index proposed to evaluate SHDs was applied to each case to obtain a threshold value that enables discernment between critical and non-critical sections using a maximum-likelihood criterion. The method was tested using 23 real cases where the reliability of the index was proved. Finally, recommendations to avoid SHDs are provided.