The results of a research effort sponsored by FHWA are summarised, the primary purpose of which was to determine the effectiveness of low-cost countermeasures in reducing accident potential at narrow bridges. The operational-based evaluation was performed by conducting before-and-after analyses of vehicle speed and lateral placement at 18 narrow bridge approach sites. The low-cost countermeasures that were evaluated consisted of combinations of advance warning signs, pavement markings, raised pavement markers, roadside delineators, type 3 object markers, and adhesive delineators. Measurements of vehicle speed and lateral placement were obtained by using the FHWA traffic evaluation system. With one exception, the operational-based effectiveness evaluation did not reveal any statistically significant differences at the 10 percent level between the sites before and after the implementation of the countermeasures. The one exception was that these countermeasures significantly reduced speed variation when all vehicle types and time periods were analysed together. For this analysis category, therefore, the low-cost countermeasures resulted in more uniform driving behaviour.
Abstract