Filomena Mauriello

Analysis of powered two-wheeler crashes in Italy by classification trees and rules discovery.

Aim of the study was the analysis of powered two-wheeler (PTW) crashes in Italy in order to detect interdependence as well as dissimilarities among crash characteristics and provide insights for the development of safety improvement strategies focused on PTWs. At this aim, data mining techniques were used to analyze the data relative to the 254,575 crashes involving PTWs occurred in Italy in the period 2006-2008. Classification trees analysis and rules discovery were performed. Tree-based methods are non-linear and non-parametric data mining tools for supervised classification and regression problems. They do not require a priori probabilistic knowledge about the phenomena under studying and consider conditional interactions among input data. Rules discovery is the identification of sets of items (i.e., crash patterns) that occur together in a given event (i.e., a crash in our study) more often than they would if they were independent of each other. Thus, the method can detect interdependence among crash characteristics. Due to the large number of patterns considered, both methods suffer from an extreme risk of finding patterns that appear due to chance alone. To overcome this problem, in our study we randomly split the sample data in two data sets and used well-established statistical practices to evaluate the statistical significance of the results. Both the classification trees and the rules discovery were effective in providing meaningful insights about PTW crash characteristics and their interdependencies. Even though in several cases different crash characteristics were highlighted, the results of the two the analysis methods were never contradictory. Furthermore, most of the findings of this study were consistent with the results of previous studies which used different analytical techniques, such as probabilistic models of crash injury severity. Basing on the analysis results, engineering countermeasures and policy initiatives to reduce PTW injuries and fatalities were singled out. The simultaneous use of classification trees and association discovery must not, however, be seen as an attempt to supplant other techniques, but as a complementary method which can be integrated into other safety analyses.

Perceptual Measures to Influence Operating Speeds and Reduce Crashes at Rural Intersections: Driving Simulator Experiment

The aim of this paper is to investigate, by means of a dynamic driving simulator experiment, the behavior of road users at rural intersections in relation to perceptual measures designed for increasing hazard detection. In the experiment 10 configurations of tangents were tested: Alt1, base tangent; Alt2, four-leg base intersection; Alt3, intersection with reduced sight distance; and Alt4 through Alt10, intersections with perceptual treatments. The Virtual Environment for Road Safety high-fidelity dynamic-driving simulator, operating at the Technology Environment Safety Transport Road Safety Laboratory located in Naples, Italy, was used. Analysis of the results used two approaches: (a) explorative description of data by cluster analysis and (b) inferential procedures about population using statistical tests. Results showed that the speed behavior in the tangents was significantly affected by the presence of the intersections and by the perceptual treatments. Intersections without perceptual treatments significantly affected driver speeds in the 250 m preceding the intersection. Perceptual treatments helped the driver to detect the intersection earlier and to slow down. Dragon teeth markings, colored intersection area, and raised median island performed better than the other perceptual treatments. They produced significant average speed reduction in the 150 m preceding the intersection ranging between 16 km/h and 23 km/h. Study results support real-world implementation of perceptual measures in rural intersections because they are low-cost, fast implementation measures with a high potential to be cost-effective.

Effects on speed and safety of point-to-point speed enforcement systems: Evaluation on the urban motorway A56 Tangenziale di Napoli

In this paper, we evaluated the effects on speed and safety of the point-to-point (P2P) speed enforcement system activated on the urban motorway A56 in Italy. The P2P speed enforcement is a relatively new approach to traffic law enforcement that involves the calculation of the average speed over a section. To evaluate the speed effects, we performed a before-after analysis of speed data investigating also effects on non-compliance to speed limits. To evaluate the safety effects, we carried out an empirical Bayes observational before-and-after study. The P2P system led to very positive effects on both speed and safety. As far as the effects on the section average travel speeds, the system yielded to a reduction in the mean speed, the 85th percentile speed, the standard deviation of speed, and the proportion of drivers exceeding the speed limits, exceeding the speed limits more than 10km/h, and exceeding the speed limits more than 20km/h. The best results were the decrease of the speed variability and the reduction of the excessive speeding behaviour. The decrease in the standard deviation of speed was 26% while the proportion of light and heavy vehicles exceeding the speed limits more than 20km/h was reduced respectively by 84 and 77%. As far as the safety effects, the P2P system yielded to a 32% reduction in the total crashes, with a lower 95% confidence limit of the estimate equal to 22%. The greatest crash reductions were in rainy weather (57%), on wet pavement (51%), on curves (49%), for single vehicle crashes (44%), and for injury crashes (37%). It is noteworthy that the system produced a statistically significant reduction of 21% in total crashes also in the part of the motorway where it was not activated, thus generating a significant spillover effect. The investigation of the effects of the P2P system on speed and safety over time allowed to develop crash modification functions where the relationship between crash modification factors and speed parameters (mean speed, 85th percentile speed, and standard deviation of speed) was expressed by a power function. Crash modification functions show that the effect of speed on safety is greater on curves and for injury crashes. Even though the study results show excellent outcomes, we must point out that the crash reduction effects decreased over time and speed, speed variability, and non-compliance to speed limits significantly increased over time. To maintain its effectiveness over time, P2P speed enforcement must be actively managed, i.e. constantly monitored and supported by appropriate sanctions.

Crash Databases in Australasia, the European Union, and the United States

Because the quality of decision making in road safety is dependent on the quality of the data on which decisions are based, efforts to improve the quality, timeliness, and accuracy of crash databases are crucial. A critical review of Australasian, European Union, and U.S. crash databases was performed, and future directions were identified. Major issues included procedures for access to crash data, crash report forms, severity of crashes reported in the databases, crash locations, crash classification, and crash severity. Access to crash databases could be provided to approved road safety professionals through a web-based portal, which could also provide detailed police crash reports. The use of electronic crash report forms was strongly recommended because it might solve most of the problems associated with paper forms. The severity of crashes reported in the databases varied across countries, and not all countries reported property-damage-only crashes. However, for both prevention and consistency between countries, collecting property-damage-only crash reports and using them to develop safety strategies is recommended. Combined use of Global Positioning System devices and geographic information systems improves the reporting of crash locations and overcomes traditional problems such as inaccuracies and collection mistakes. To develop effective countermeasures, it is recommended that crashes be classified by the maneuvers and sequence of events for each traffic unit. The adoption of the same system for crash severity classification in different countries would allow comparisons in safety performance between countries and jurisdictions.

Prediction of Drivers' Speed Behavior on Rural Motorways Based on an Instrumented Vehicle Study

Several studies have developed operating speed prediction models. Most of the models are based on spot speed data, collected by radar guns, pavement sensors, and similar mechanisms. Unfortunately, these data collection methods force the users to assume some invalid assumptions in driver behavior modeling: constant operating speed throughout horizontal curves and occurrence of acceleration and deceleration only on tangents. In this study, an instrumented vehicle with GPS continuous speed tracking was used to analyze driver behavior in terms of speed choice and deceleration or acceleration performance and to develop operating speed prediction models. The data used in the study were from a field experiment conducted in Italy on the rural motorway A16 (Naples–Avellino). Models were developed to predict operating speed in curves and tangents, deceleration and acceleration rates to be used in the operating speed profiles, starting and ending points of constant operating speed in a curve, 85th percentile of the deceleration and acceleration rates of individual drivers, and 85th percentile of the individual drivers’ maximum speed reduction in the tangent-to-curve transition. The study results showed that (a) the drivers’ speed was not constant along curves, (b) the individual drivers’ maximum speed reduction was greater than the operating speed difference in the tangent-to-curve transition, and (c) the deceleration and acceleration rates experienced by individual drivers were greater than the deceleration and acceleration rates used to draw operating speed profiles.

Procedure for Ranking Unsignalized Rural Intersections for Safety Improvement

This paper presents a procedure for ranking rural unsignalized intersections that uses quantitative safety evaluations performed as part of the safety inspection process. The procedure might be effective for the selection of cost-effective treatments at intersections and might be quite helpful for administrations that do not have high-quality crash data and for those that manage low-volume roads for which crash data cannot give enough information to help prevent future crashes. The procedure evaluates a safety index (SI) that can be used to rank intersections for further investigation. The SI can be assessed whether crash data are available or not. If crash data are available and their quality is good, the SI can be effectively used in conjunction with the empirical Bayes (EB) estimate of frequency as ranking criteria. If crash data are not available or poor, the SI can be used as a proxy for crash data and becomes the only ranking criterion. Validation of the SI procedure was performed by comparing the results with EB safety estimates. The SI was assessed in 22 three-leg intersections in Italy. In the same intersections, a safety performance function was calibrated and the EB refinement technique was used to obtain a better estimate of existing safety performance. Correlation between SI values and EB safety estimates was highly significant, with 84% of the variation in the estimated number of crashes explained by the SI value. The results from a Spearmans rank correlation show that rankings from the SI and the EB estimate agree at the 99.9% significance level.

Effects of traffic control devices on rural curve driving behavior

This study investigated, by means of a dynamic driving simulator experiment, driver behavior at curves on rural two-lane highways in relation to different advance warning signs, perceptual measures, and delineation treatments. The tested treatments were intended to alert drivers to the presence of low-radius curves and to affect their behavior in the approach to the curve as well as along the curve itself. The study results showed that the advance warning signs, perceptual measures, and delineation treatments tested in the driving simulator experiment produced significant effects on driver behavior. The perceptual treatments (i.e., colored transverse strips, dragon teeth markings, colored median island) were the most effective treatments because they produced significant speed reductions in the approach tangent as well as inside the curve. Deceleration behavior in the approach to the curve was affected significantly by the presence of treatments that helped drivers to detect the curve earlier; early detection provided more time to perform deceleration maneuvers at lower rates. The study results strongly supported the real-world implementation of colored transverse strips, dragon teeth markings, and the colored median island. Implementation of the tested measures should be conducted on similar rural highways to validate general application of the results of this study to other regions.