Grazia La Cava

The methodological approach to safety evaluation of two-lane rural highway segments that is presented uses both analytical procedures referring to alignment design consistency models and safety inspection processes. A safety index (SI) that quantitatively measures the relative safety performance of a road segment is calculated from the procedure. The SI is formulated by combining three components of risk: the exposure of road users to road hazards, the probability of a vehicle's being involved in an accident, and the resulting consequences should an accident occur. This systematic and replicable procedure integrates two different, complementary approaches-one based on design consistency evaluations and the other on safety inspections-and makes it possible to address a wide variety of safety issues effectively. A further advantage of the procedure is its applicability on highways where crash data are either not available or unreliable. Validation of the procedure was carri ed out o n a sample of roads by a comparison of the risk rank obtained by using the SI and accident history. The SI was assessed in 30 segments chosen from a sample of two-lane rural highways in Italy, and the actual accident situation was obtained with the empirica! Bayes (EB) procedure. Spearman's rank correlation was used to determine the leve! of agreement between the rankings obtained with the two techniques. The results from the Spearman's rank-correlation analysis validate the SI, indicating that the ranking from the SI scores and the EB estimates agrees at the 99.9% leve! of significance with a correlation coefficient of 0.87. Road safety evaluations on low-and medium-traffic rural two-lane highways can raise concems due to both the general defìciency of reliable data on road accidents and the circurnstance that few accident data can always give enough information on accidents to be prevented. O n the basis of these considerations, a methodological approach was defìned for the safety evaluation of two-lane rural highways that uses both analytical procedures referring to alignment design consistency models and safety inspection processes. The research was performed as part of the project ldentifìcation of Hazard Locations and Ranking of Measures to Irnprove Safety o n Local Rural Roads (ltalian acronym IASP), funded by the European Comrnission (Directorate Generai) and the Province of Catania in Italy (1-5). Many studies show that safety evaluations based on the analysis of alignment design consistency can be effective in identify-136 ing hazardous road locations (6, 7). The proposed approach uses theoretical-experimental models for the evaluation of alignment design consistency. However, the resulting analyses, although effective in addressing alignment inconsistencies, do not highlight all the potenti al accident contributory factors. Hence, the IASP methodology integrates the results ofthe models with those deriving from the safety issue evaluation made during the safety inspection process. Road safety inspections (RSis) are aimed at identifying potential hazards, which are assessed by measuring risk in relation to those road features that may Iead to future accidents so that remedial treatments may be implemented before accidents happen (8). Safety inspections are recognized as an effective tool andare becoming an accepted practice in many agencies around the world (9-14). Recent research performed in British Columbia (15) and in ltaly (8, 16) has shown that road safety impact assessments based on RSis can be effective. T o use safety inspections as part of a quantitative safety evaluation process, the IASP project defìned procedures and criteria for identifying and ranking safety issues (2). The ranking criteria take into account the road safety effects of the identifìed issues. The RSI carried out according to these procedures showed that there is a statistically signifìcant level of agreement (measured through the k-test) between the safety issue evaluations produced by different inspectors for the majority of the safety issues. A systematic and replicable safety inspection process allows a quantitative safety index (SI) to be assessed based on the data obtained from the RSI combined with information from theoretical-experimental models. FORMULATION OF SI The SI measures the relative safety performance of a road segment. l t does not take into accountjunctions, and i t refers to two-lane rural highways. The SI is formulated by combining three components of risk: the exposure of road users to road hazards (exposure factor) , the probability of a vehicle' s being involved in an accident (accident frequency factor), and the resulting consequences, should an accident occur (accident severity factor). The genera! formulation for the SI is as follows: SI = exposure factor x accident frequency factor x accident severity factor Exposure Factor (l) The exposure factor measures the exposure of road users to road hazards and is assessed as follows :

Abstract We describe a simple framework for classifying road accidents using a fuzzy algorithm. Moreover, we study the role that the road conditions and environment have on road accidents. We classify accidents according to their causes using a fuzzy algorithm through a computerised procedure and a simplified model. The experimental study can be used as an instrument for identification of road failures or potential road environment influences on road safety. Using the fuzzy algorithm k-nn, we were able to produce a ...