1,720,994 research outputs found
Procedure for Ranking Unsignalized Rural Intersections for Safety Improvement
No full textThe paper presents a ranking procedure for rural unsignalized intersections which uses quantitative safety evaluations performed as part of the safety inspection process. It might be effective for the selection of cost effective treatments at intersections and might be very helpful for administrations which do not have quality crash data and for administrations which manage low volume roads where crash data cannot give enough information on crashes to be prevented.
The procedure evaluates a safety index (SI) that can be used to rank intersections for further investigations. SI can be assessed whether crash data are available or not. If crash data are available and their quality is good, SI can be effectively used in conjunction with the EB estimate of frequency as ranking criteria. If crash data are not available or poor, SI can be used as a proxy of crash data and becomes the only ranking criteria.
Validation of the safety index procedure was carried out by comparing the results with the EB safety estimates. The SI was assessed in twenty-two 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 the existing safety performance. Correlation between SI values and EB safety estimates is highly significant, with 84% of the variation in the estimated number of crashes explained by the SI value. The results from the Spearman's rank-correlation show that ranking from the SI and the EB estimate do agree at the 99.9% significance level
Effects on speed and safety of point-to-point speed enforcement systems: evaluation on the urban motorway A56 Tangenziale di Napoli
No full textIn 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
Data mining techniques for exploratory analysis of pedestrian crashes
No full textExploratory analysis was made of data from pedestrian crashes to detect interdependence and dissimilarities between crash patterns and to provide insight for the development of safety improvement strategies focused on pedestrians. Data-mining techniques, such as classification trees and association rules, were used on data related to 56,014 pedestrian crashes that occurred in Italy from 2006 to 2008. Crash severity was the response variable most sensitive to crash patterns. The most influential crash patterns were road type, pedestrian age, lighting conditions, vehicle type, and interactions between these patterns. Notable results included associations between fatal crashes and rural areas, urban provincial and national roads, pedestrians older than 75 years, nighttime conditions, pedestrians older than 65 years in nighttime crashes, drivers' young age and male gender in nighttime crashes, and truck involvement. To mitigate the fatal crash patterns identified by the classification trees and association rules, several measures are suggested for implementation. Results of the study are consistent with results of previous studies that used other analytic techniques, such as probabilistic models of crash injury severity. The data-mining techniques used in the study were able to detect interdependencies among crash characteristics. The use of classification trees and association rules, however, must be seen not as an attempt to supplant other techniques, but as a complementary method that can be integrated into other safety analyses
Traffic calming along rural highways crossing small urban communities: driving simulator experiment
No full textThe paper investigated drivers’ speed behaviour in a section of a rural highway crossing a small urban community in the existing scenario without any traffic calming device and in two different design scenarios with traffic calming in the urban community. Two gateways and four integrative traffic calming devices along the route within the urban area were tested. The gateways were aimed at slowing down the vehicles entering in the built-up area, while the traffic calming devices were aimed at complementing
the gateway effect inside the built-up area. Two design options were tested: first option (alt1) is a combination of low cost measures, whereas the second option (alt2) is more expensive as includes a chicane and requires land acquisition.
Drivers’ behaviour was investigated by means of a driving simulator experiment. The VERA dynamicdriving simulator operating at the TEST Road Safety Laboratory located in Naples (Italy) was used.
Simulation results were validated by the comparison of speed behaviour in the real world and in the driving simulator, in the scenario without traffic calming.
Analysis of the driving simulator experiment results was performed using two different approaches:
(a) explorative description of data by cluster analysis; (b) inferential procedures about population using statistical tests. Cluster analysis was carried out in order to test if the drivers’ speed behaviour in the different design alternatives was substantially different. Statistical tests were performed in order to
verify if speeds in specific sections were significantly different. Cluster analysis looked at speed profiles, whereas statistical tests looked at speed data in specific points.
The obtained results showed a different behaviour of drivers approaching the urban community in the existing scenario and in the design scenarios. In the south direction, mean speed reduction ranging between 16 and 17 km/h, with 5% level of significance, was observed. In the north direction, mean speed reduction equal to 11 km/h, with 10% level of significance, was observed. Differences between the two design alternatives were not statistically significant. Along the urban community, a statistically significant mean speed reduction ranging between 9 and 15 km/h was observed in the south direction. In the north
direction, speed reduction was not statistically significant.
Overall, combined results of cluster analysis and statistical tests showed that the treatments were more effective in the direction with higher speeds in the base scenario
Low-cost measures for reducing speeds at curves on two-lane rural highways
No full textThis paper investigated, by means of a dynamic driving-simulator experiment, drivers' 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 curves, prompting a reduction in curve approach speeds, and to affect drivers' speed as they drove through curves. A benefit-cost analysis was performed to determine the economic feasibility of applying the countermeasures to speeding tested in the driving simulator. Study results showed that all the treatments produced significant effects on drivers' speed behavior at curves on rural two-lane highways. The perceptual treatments (i.e., colored transverse strips, dragon-teeth markings, and colored median island) were the most effective. The safety benefits measured in lower crash costs arising from speed reductions were much greater than the costs of the alternatives. The most cost-effective treatment was the curve warning sign because of the lower cost. However, colored transverse strips and dragon-teeth markings produced higher benefits and were highly cost-effective for average daily traffic greater than 1,000 vehicles per day. The study results strongly support real-world implementation of colored transverse strips, dragon-teeth markings, and the colored median island
Classification Trees and Association Rules for Exploratory Analysis of Powered Two-Wheeler Crashes
No full textPoint-to-point speed enforcement systems: Speed limits design criteria and analysis of drivers’ compliance
No full textPoint-to-point (P2P) speed enforcement is a relatively new approach to traffic law enforcement. Its technology allows vehicles whose average speed exceeds the speed limit over the controlled section to be fined. It therefore encourages compliance over distances longer than those where spot enforcement policies have been in place.In this paper, a procedure for consistently setting speed limits with such enforcement systems is proposed. Such a method has been applied to design the speed limits on two motorways in the district of Naples, Italy, where P2P enforcement systems became operational in 2009 and 2010. The speed limits, which were set using the Italian geometric design standard to assess vehicle stability and stopping sight distance, have been compared with those provided by using well-known international standards.The impact of the newly designed speed limits and of the P2P enforcement system on drivers' speeding behaviour has been quantified for each highway section and vehicle type. In fact, accurate measurements of the average travel speeds of each vehicle crossing the enforced sections, before and after the activation of the system, were available. The migration from the old speed limits with spot speed enforcement to the new approach resulted in a notable increase in drivers' compliance to the speed limits with a remarkable decrease in both the average of individual speeds and in their standard deviation.In addition, the analysis of 3. years of data shows that a gradual adaptation of drivers' behaviour to the system took place. In particular, a decreasing compliance to the speed limits points to a non-optimal system management. Finally, the results of a revealed preference survey allowed us to make a behavioural interpretation regarding the significantly different impacts measured on the two motorways
Effects of Traffic Control Devices on Rural Curve Driving Behavior
No full textThis 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
Continuous Speed Profiles to Investigate Drivers' Behaviour on Two-lane Rural Highways
No full textTo improve design consistency, several studies developed operating speed prediction models and investigated drivers’ speed behaviour. Most of the existing models are based on spot speed data assuming constant operating speed throughout the horizontal curves and occurrence of acceleration and deceleration only on tangents. To overcome limitations associated with these hypotheses, this study investigated continuous speed profiles by a driving simulator experiment carried out on a two-lane rural highway using the VERA high-fidelity dynamic-driving simulator.
A piecewise linear regression model and locally weighted regression scatterplot smoothing were used to remove the noise in the data set while preserving underlying patterns and to identify the significant changes in the speed profile. Based on the smoothed speed profiles, models to predict operating speed in curves and in tangents, deceleration and acceleration rates to be used in the operating speed profiles, and starting and ending points of constant operating speed in curve were developed. Notably, radius of the curve affects not only the operating speed in the curve but also the operating speed of the tangent following the curve. The smaller the radius, the lower the operating speed on the exit tangent. Both acceleration and deceleration rates increase with curvature, which is the reciprocal of radius. An important result of our study is that the operating speed is not constant along the curves. On small radius curves, deceleration ends close to the center of the curve and acceleration starts close to the end of the curve. Increasing the curve radius, the endpoint of deceleration moves towards the beginning of the curve whereas the acceleration beginning moves towards the center of the curve. Conversely, and also noteworthy, the speed differential between an approach tangent and a horizontal curve (tangent-to-curve speed differential), the consistency measure with the greatest safety effect, is higher when long tangents are preceded by curves with large radius
Analysis of powered two-wheeler crashes in Italy by classification trees and rules discovery
No full textAim 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 analyse
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