Grazia La Cava

Safety Index for Evaluation of Two-Lane Rural Highways

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 vehicles 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 carried out on 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 empirical Bayes (EB) procedure. Spearmans rank correlation was used to determine the level of agreement between the rankings obtained with the two techniques. The results from the Spearmans rank-correlation analysis validate the SI, indicating that the ranking from the SI scores and the EB estimates agrees at the 99.9% level of significance with a correlation coefficient of 0.87.

Driving Performance, Alignment Consistency, and Road Safety: Real-World Experiment

Road infrastructure improvement is one of the three pillars in the European Union policy aimed at halving the number of fatalities in road accidents by 2010. Increased knowledge and experience have proved that highway consistency analysis is an effective tool in the evaluation of road performance in terms of safety. Recent studies have attempted to provide information relating to the geometric consistency of road alignment by using different approaches based on geometric relation design, differential between design and operating speed, driving performance with instrumented vehicles, and human workload evaluation. This paper presents the results of a naturalistic driving experiment carried out with the University of Catanias Driving Instrumented Vehicle Acquisition System–instrumented vehicle. Representative variables for describing alignment consistency were defined and collected by direct measurement during real-world driving tests. From the seven parameters taken into consideration, the maximum driving speed differential between two successive elements and between the average section speed and the minimum single element speed were chosen as driving performance indicators (DPIs), since they are not correlated and agree statistically with the accident history. On the basis of actual driving behavior by means of DPIs, design inconsistencies were identified along different test courses, and their agreement with safety evaluation criteria and relation design parameters was verified. Comparison analyses among DPIs, speed consistency variables, and relation design parameters have evidenced the effectiveness of the indirect measurement of design consistency and the possibility of defining threshold values for the identification of those elements characterized by acceptable (good), reasonable (fair), or intolerable (poor) alignment inconsistencies.

Actual Driving Data Analysis for Design Consistency Evaluation

In recent years, researchers have proved that a consistent highway design ensures that successive elements are coordinated to produce harmonious and homogeneous driver performances and does not provoke unexpected events. Knowledge and practice show that drivers make fewer errors near geometric features that conform to their expectations. On this basis, the importance of identifying inconsistencies on highways for its significant contribution to road safety is emerging as an important feature in highway design. Although several techniques and models for evaluating the consistency of a design in a quantitative way have been identified and some countries have implemented the design consistency concept in their road design guidelines mainly in a qualitative way, there have been only a few efforts to measure actual driving behavior. The aim of this paper was to determine design inconsistencies on existing two-lane rural roads with the use of actual driving behavior by means of field data measurements and to verify their agreement with a consistency evaluation model. Furthermore, suitable equipment and a procedure for surveying driving dynamics and driver workload have been developed. In particular, driving behavior was assessed through direct measurements and parameters taken from data collected on a selected sample of test drivers by using a purposely designed instrumented vehicle. The vehicle, named the driver instrumented vehicle acquisition system (DIVAS), was driven under real traffic conditions on a two-lane rural road. The design classes of consistency of the test courses also were evaluated with a well-known safety criteria model. Data collection and treatment procedures are presented, and data analysis and results from this first experiment are given.

Safety Inspections as Supporting Tool for Safety Management of Low-Volume Roads

Road safety inspections (RSIs) are becoming an accepted practice in many agencies around the world. A safety assessment procedure based on safety inspections that can be used as a supporting tool in the safety management of low-volume rural roads is presented. From the procedure, a safety index (SI) that quantitatively measures the relative safety performance of a road segment is calculated. The RSIs carried out according to the defined procedures showed that, for the majority of the safety issues, there was a statistically significant level of agreement on the ranking of the issues produced by different inspectors. Further, the SI was assessed in 30 segments of two-lane rural roads, and rankings performed according to the SI scores and according to the empirical Bayes (EB) safety estimates were compared. This comparison showed a good correlation between SI and EB estimates. The results from the Spearmans rank correlation analysis provide additional validation of the procedure, indicating that the rankings from the SI scores and the EB estimates agreed at the 99.9% level of significance. The SI can be assessed as part of the safety inspection process without relevant supplementary work. The low cost and applicability in road networks where geometric and crash data are not available make the procedure very attractive for low-volume roads.

Fuzzy model for safety evaluation process of new and old roads

More than 50% of traffic fatalities occur on two-lane rural roads, and more than half of these fatalities occur on curved roadway sections. A large body of research can be used to analyze and evaluate the fundamental relationships between accident situation, highway geometric design, driving behavior, and driving dynamics. These factors form the basis for the development of three quantitative safety criteria used to evaluate the hazards of two-lane rural roads with respect to new designs; redesigns; restoration, rehabilitation, or resurfacing projects; and existing alignments. The safety criteria support the design engineer in classifying new or old roadway sections according to good (sound), fair (tolerable), and poor (dangerous) design practices. On the basis of observation of the actual variation in the accident rate with respect to road alignment, a fuzzy model was developed to classify roadway elements by using these safety criteria to obtain a more careful evaluation of highway design inconsistencies. For each criterion, the inconsistencies were included in three fuzzy sets (good, fair, poor) with differing degrees of membership. By defining linear membership functions, it was possible to obtain good results to classify road sections and then to determine a prioritization scale of maintenance interventions. The procedure can be applied to large databases of road networks to identify the more dangerous design elements that need interventions to improve highway safety and to allocate resources under limited budget conditions.

Seismic Risk Assessment of the Rural Road Network

The effects of seismic events on the interruption of the road network and the consequent reduction of what remain available greatly affect the overall performance of the system. This requires a seismic risk analysis of the road system which is able to evaluate the effects of earthquakes beforehand in order to define a priority ranking for maintenance and seismic retrofit programs. This paper will propose a methodology for the evaluation of seismic risk on rural road networks. A model used to define the risk level of the road lifelines is based on three factors: area seismic hazard, road link seismic exposure, and bridge seismic vulnerability.