The Portuguese Road Administration adopted recently a new system for the detection of inconsistent horizontal curves in single carriageway rural roads of the National Road Network, and for the improvement of their safety records. This system resulted from research carried out within the research program of the National Laboratory for Civil Engineering (LNEC) and the European Research Program TRANSPORT of the European Union's Fourth Framework Program (SAFESTAR project). These investigations were followed by a specific study at LNEC, aiming at the development of application procedures as regards the Portuguese road network conditions. Models for calculation of unimpeded speed profiles are used to estimate conformance of horizontal curves with driver expectancy and to assess the increase in their accident risk, as compared with the accident risk on tangents. Predictions of accident rates on curves and on tangents are made using log-linear accident frequency models, with speed estimates and selected measured road characteristics as explanatory variables. Energy considerations and the change in the expected injury accident rates are used to classify horizontal curves in four consistency classes. A computer program was developed for practical application of this process. In addition, for each consistency class, a systematic curve treatment was defined and is currently being carried out in several roads. Generally, this treatment involves such low cost engineering measures as marking, signing and shoulder improvement. The safety record of the consistency classes is discussed, based on five years of accident data on the Portuguese main road network.
Samenvatting