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PubMed2005

Identifying significant predictors of injury severity in traffic accidents using a series of artificial neural networks.

Understanding the circumstances under which drivers and passengers are more likely to be killed or more severely injured in an automobile accident can help improve the overall driving safety situation. Factors that affect the risk of increased injury of occupants in the event of an automotive accident include demographic or behavioral characteristics of the person, environmental factors and roadway conditions at the time of the accident occurrence, technical characteristics of the vehicle itself, among others. This study uses a series of artificial neural networks to model the potentially non-linear relationships between the injury severity levels and crash-related factors. It then conducts sensitivity analysis on the trained neural network models to identify the prioritized importance of crash-related factors as they apply to different injury severity levels. In the process, the problem of five-class prediction is decomposed into a set of binary prediction models (using a nationally representative sample of 30358 police-recorded crash reports) in order to obtain the granularity of information needed to identify the "true" cause and effect relationships between the crash-related factors and different levels of injury severity. The results, mostly validated by the findings of previous studies, provide insight into the changing importance of crash factors with the changing injury severity levels.

Accidents, Traffic↗

PubMed2005

Safety impact of engineering treatments on undivided rural roads.

This article presents an evaluation of the safety impacts of four engineering treatments implemented in the Autonomous Community of Madrid (Spain): highway upgrading; updating and improvement of traffic signing; repainting of pavement markings and pavement resurfacings. This evaluation was carried out using the Empirical Bayes method with a comparison group. The functioning of a methodology to test the significance of the safety impact is described. The results show that highway upgrading has a positive and significant safety impact, while the updating and improvement of traffic signing, the repainting of road markings and pavement resurfacings do not exhibit a significant impact on safety.

Accidents, Traffic↗

PubMed2005

A method for identifying rear-end collision risks using inductive loop detectors.

An innovative feature of this study is to firstly attempt to capture rear-end collision potentials from the analysis of inductive loop detector data. Signals collected from loops are applied for monitoring individual vehicle information on freeways to estimate safe stopping distances in car-following situations. An index to quantify the potential of rear-end collisions is derived, and further employed for developing criteria to evaluate levels of rear-end collision risks. The proposed methodology based on loop detector data enables to identify collision potentials in real time. It is believed that the index would be a valuable tool for operating agencies in developing various strategies and policies toward enhancements of traffic safety.

Accidents, Traffic↗

PubMed2005

Quantifying effects of ramp metering on freeway safety.

This study presents a real-time crash prediction model and uses this model to investigate the effect of the local traffic-responsive ramp metering strategy on freeway safety. Safety benefits of ramp metering are quantified in terms of the reduced crash potential estimated by the real-time crash prediction model. Driver responses to ramp metering and the consequent traffic flow changes were observed using a microscopic traffic simulation model and crash potential was estimated for a 14.8 km section of I-880 in Hayward, California and a hypothetical isolated on-ramp network. The results showed that ramp metering reduced crash potential by 5-37% compared to the no-control case. It was found that safety benefits of local ramp metering strategy were only restricted to the freeway sections in the vicinity of the ramp, and were highly dependent on the existing traffic conditions and the spatial extent over which the evaluation was conducted. The results provide some insight into how a local ramp metering strategy can be modified to improve safety (by reducing total crash potential) on longer stretch of freeways over a wide range of traffic conditions.

Accidents, Traffic↗

PubMed2005

Safe pedestrian crossings for children and elderly.

In May 2000, the Swedish code governing the conduct of drivers at marked crosswalks became stricter with the intent to improve safety and mobility for pedestrians. A crash analysis based on a macro study of all of Sweden suggests that the injury risk in marked, not reconstructed, crosswalks increased by 27% for pedestrians and 19% for bicyclists. The reason for this may be that pedestrians get a false sense of safety with the new code. Reconstructions aiming at lowering speeds are indeed needed for the change of code to be positive. The 90-percentile speed should not exceed 30 km/h or safety will deteriorate. However, low speed by itself may not guarantee optimal safety. Safety can be further improved at sites, which already have been reconstructed to ensure low speeds. Results based on field data collected at sites close to schools in Malmö, Trollhättan and Borås in Sweden, and in-depth studies and other analyses of Finnish and Swedish police-reported crashes, suggest that safety of children and elderly is further improved at sites where visibility, orientation and clarity are sufficient. Also, marking crosswalks may increase yield rates (expected improvement 6%) towards pedestrians; and speed cushions situated at a longer distance from the marked crosswalk increase yield rates towards pedestrians and cyclists compared to speed cushions closer by.

Accidents, Traffic↗

PubMed2005

Does public education improve rail-highway crossing safety?

Improvements in rail-highway grade crossing safety have resulted from engineering, law enforcement, and educating the public about the risks and the actions they should take. The primary form of the latter is a campaign called Operation Lifesaver which started in the 1970s. This paper uses a negative binomial regression to estimate whether variations in Operation Lifesaver activity across states and from year-to-year in individual states are related to the number of collisions and fatalities at crossings. Annual data on the experience in 46 states from 1996 to 2002 are used. The analysis finds that increasing the amount of educational activity will reduce the number of collisions with a point elasticity of -0.11, but the effect on the number of deaths cannot be concluded with statistical certainty.

Accidents, Traffic↗

PubMed2005

Evaluation of variable speed limits for real-time freeway safety improvement.

Use of various variable speed limit (VSL) strategies as a tool for safety improvement on freeways was evaluated using simulation of a section of Interstate 4 in Orlando, FL. Real-time crash likelihood was calculated based on models developed in previous research by the first author [Abdel-Aty, M., Uddin, N., Pande, A., January 2005. Split models for predicting multi-vehicle crashes during high-speed and low-speed operating conditions on freeways. In: Presented at the 84th Annual Meeting of the Transportation Research Board, Washington, DC]. VSL implementation produced safety improvement by simultaneously implementing lower speed limits upstream and higher speed limits downstream of the location where crash likelihood is observed in real-time. This improvement was realized in the case of medium-to-high-speed regimes on the freeway, but no benefit was achieved in low-speed situations (no substantial safety benefit from implementing VSL in congested situation's simulation). The final recommendations for implementing VSL are: gradually introducing speed limit changes over time (5 mph every 10 min); abruptly changing speed limit in space ( no gap distance); reducing speed limits upstream and increasing speed limits downstream of location of interest; the speed limit changes up- and downstream should be large in magnitude (15 mph) and implemented within short distances (2 miles) of the location of interest. In addition to the safety benefit, this final strategy also produced travel time savings.

Accidents, Traffic↗

PubMed2005

Safety and accessibility effects of code modifications and traffic calming of an arterial road.

The European Road E12 through the community center of Storuman, Sweden was reconstructed in 1999 and 2000. Pedestrian walkways, traffic islands, chicanes of a type referred to as "Danish buns", a roundabout and a two-directional cycle track along the E12 were installed. The purpose of the reconstruction was to improve safety for pedestrians and bicyclists, primarily for children, the elderly and the disabled, and to reduce the barrier effect of the E12 thoroughfare. In May 2000, the code governing the conduct of drivers at marked crosswalks in Sweden became stricter to improve safety and mobility for pedestrians. The combined effect of reconstructions and change of code was analyzed. Traffic behavior was studied at the intersection where the roundabout was constructed. Yield behavior towards pedestrians changed significantly. The difference was even greater with respect to yielding to child bicyclists - from 6% before to 84% after - even though the code change only related to pedestrians. Crash data analysis suggests a minor increase in fall injuries after reconstructions and change of code. Measures of speed, behavioral studies, questionnaires, face-to-face interviews and crash data analysis suggest that safety has increased not only along the E12 but also along adjacent roads. The final conclusion is that a bypass is not needed in a case like Storuman. Traffic calming of the main arterial through the town seems sufficient.

Accidents, Traffic↗

PubMed2006

Explicit and implicit processes in behavioural adaptation to road width.

The finding that drivers may react to safety interventions in a way that is contrary to what was intended is the phenomenon of behavioural adaptation. This phenomenon has been demonstrated across various safety interventions and has serious implications for road safety programs the world over. The present research used a driving simulator to assess behavioural adaptation in drivers' speed and lateral displacement in response to manipulations of road width. Of interest was whether behavioural adaptation would occur and whether we could determine whether it was the result of explicit, conscious decisions or implicit perceptual processes. The results supported an implicit, zero perceived risk model of behavioural adaptation with reduced speeds on a narrowed road accompanied by increased ratings of risk and a marked inability of the participants to identify that any change in road width had occurred.

Acceleration↗

PubMed2006

Spatial analysis of fatal and injury crashes in Pennsylvania.

Using injury and fatal crash data for Pennsylvania for 1996-2000, full Bayes (FB) hierarchical models (with spatial and temporal effects and space-time interactions) are compared to traditional negative binomial (NB) estimates of annual county-level crash frequency. Covariates include socio-demographics, weather conditions, transportation infrastructure and amount of travel. FB hierarchical models are generally consistent with the NB estimates. Counties with a higher percentage of the population under poverty level, higher percentage of their population in age groups 0-14, 15-24, and over 64 and those with increased road mileage and road density have significantly increased crash risk. Total precipitation is significant and positive in the NB models, but not significant with FB. Spatial correlation, time trend, and space-time interactions are significant in the FB injury crash models. County-level FB models reveal the existence of spatial correlation in crash data and provide a mechanism to quantify, and reduce the effect of, this correlation. Addressing spatial correlation is likely to be even more important in road segment and intersection-level crash models, where spatial correlation is likely to be even more pronounced.

Accidents, Traffic↗

PubMed2006

Young driver accidents in the UK: the influence of age, experience, and time of day.

Young drivers, especially males, have relatively more accidents than other drivers. Young driver accidents also have somewhat different characteristics to those of other drivers; they include single vehicle accidents involving loss of control; excess speed for conditions; accidents during darkness; accidents on single carriageway rural roads; and accidents while making cross-flow turns (i.e. turning right in the UK, equivalent to a left turn in the US and continental Europe). A sample of over 3000 accident cases was considered from midland British police forces, involving drivers aged 17-25 years, and covering a two year period. Four types of accident were analysed: right-turns; rear-end shunts; loss of control on curves; and accidents in darkness. Loss of control on curves and accidents in darkness were found to be a particular problem for younger drivers. It was found that cross-flow turn accidents showed the quickest improvement with increasing driver experience, whereas accidents occurring in darkness with no street lighting showed the slowest rate of improvement. 'Time of day' analyses suggested that the problems of accidents in darkness are not a matter of visibility, but a consequence of the way young drivers use the roads at night. There appears to be a large number of accidents associated with voluntary risk-taking behaviours of young drivers in 'recreational' driving.

Accidents, Traffic↗

PubMed2006

Segmentation of lines based on point densities--an optimisation of wildlife warning sign placement in southern Finland.

Current and previous placement of wildlife warning signs by the Finnish Road Administration is based on suggestions from hunting associations and individuals. The problem within this practice is that the placement of warning signs is not a transparent process. Within this paper, we evaluate the current placement of wildlife warning signs for the Uusimaa region in southern Finland and develop a method to optimise warning sign placement using kernel density estimations, which are based on existing wildlife-vehicle accident records. The contour lines of these densities can indicate the road sections to be marked with warning signs. To apply a well-documented computational method, based on these moose and white-tailed deer accident locations, assists the Finnish Road Administration in their task to place, replace and assess wildlife-warning signs for specific road sections.

Accident Prevention↗

PubMed2006

The influence of perceptual speed regulation on speed perception, choice, and control: tunnel wall characteristics and influences.

The present work sought to determine if the type of visual pattern and presence of texture applied to transportation tunnel walls differentially affected driving performance. Choice of speed and speed control were measured with 32 participants who drove through a simulated transportation tunnel environment. Participants experienced three visual patterns consisting of vertical segments that decreased, increased, and remained a constant width throughout the length of the tunnel. Participants also drove a baseline control condition in which no visual pattern was present. Each of these conditions was presented either with or without a homogenous texture. When compared to the baseline condition, results indicated drivers gradually decreased speed when exposed to the decreasing width visual pattern and increased speed with the increasing width visual pattern. The presence of texture served to attenuate overall driving speed. Results suggest drivers' perception of speed and their subsequent response to such perceptions were modified by the visual pattern and texture expressed on the tunnel wall. The evident speed control opportunities afforded to the traffic engineer are discussed.

Acceleration↗

PubMed2006

Modeling crash outcome probabilities at rural intersections: application of hierarchical binomial logistic models.

It is important to examine the nature of the relationships between roadway, environmental, and traffic factors and motor vehicle crashes, with the aim to improve the collective understanding of causal mechanisms involved in crashes and to better predict their occurrence. Statistical models of motor vehicle crashes are one path of inquiry often used to gain these initial insights. Recent efforts have focused on the estimation of negative binomial and Poisson regression models (and related deviants) due to their relatively good fit to crash data. Of course analysts constantly seek methods that offer greater consistency with the data generating mechanism (motor vehicle crashes in this case), provide better statistical fit, and provide insight into data structure that was previously unavailable. One such opportunity exists with some types of crash data, in particular crash-level data that are collected across roadway segments, intersections, etc. It is argued in this paper that some crash data possess hierarchical structure that has not routinely been exploited. This paper describes the application of binomial multilevel models of crash types using 548 motor vehicle crashes collected from 91 two-lane rural intersections in the state of Georgia. Crash prediction models are estimated for angle, rear-end, and sideswipe (both same direction and opposite direction) crashes. The contributions of the paper are the realization of hierarchical data structure and the application of a theoretically appealing and suitable analysis approach for multilevel data, yielding insights into intersection-related crashes by crash type.

Accidents, Traffic↗

PubMed2006

Driver behaviour, dilemma zone and safety effects at urban signalized intersections in Greece.

Driving behaviour at signalized intersections is one of the main factors contributing to the safety level of such entities. This behaviour, with respect to yellow signal obedience or violation, is examined at a signalized intersection in Thessaloniki, Greece. The data, collected for the study purposes, include vehicles' speeds and distance from stop line when exposed to yellow light, gender and age group of drivers as well as reaction of Platoon leaders and first followers. Drivers were grouped into three categories, namely conservative, normal and aggressive, according to their behaviour at the intersection, the existence of a dilemma or option zone and their initial approaching speed. A binary choice model was also developed relating the probability of stopping at the STOP line or crossing it as a function of approach speed, distance from intersection, gender, age group and the existence or not of a dilemma zone. The findings of this research indicate that a large percentage of drivers facing the yellow signal are caught in a dilemma zone due to high approaching speeds and exercise an aggressive behaviour. The distribution of drivers into the three categories changes with differing assumptions pertaining to the factors affecting the calculation of safe stopping distance and critical crossing distance as well as speed thresholds for determining a priori aggressive behaviour. The research concludes that aggressive drivers represent a high percentage of all drivers and measures towards improving driving behaviour and/or reducing vehicles' speeds are required.

Acceleration↗

PubMed2006

Safety effects of roundabouts in Flanders: signal type, speed limits and vulnerable road users.

This paper examines the road safety effects of roundabouts built in Flanders between 1994 and 2000. While the overall effect is positive (39% reduction of injury accidents), the results vary considerably with the speed limit on the main and adjacent road (the higher, the more effective) and the pre-roundabout signalization of the intersection (32% reduction with traffic lights versus 44% without). However, microscopic analysis reveals that roundabouts are not always effective. Serious injury accidents are estimated to increase by 117% on 70 km/h x 50 km/h intersections equipped with signalization before the roundabout. The number of injury accidents involving vulnerable road users is also found to increase (28%) on 50 km/h x 50 km/h junctions that were originally signalized. Moreover, the vulnerable road user is more likely to get fatally or seriously injured. Therefore, it is concluded that traffic lights protect vulnerable road users more effectively than roundabouts, which, in turn, are superior to intersections without signalization.

Acceleration↗

PubMed2006

Determining the potential safety benefit of improved lighting in three pedestrian crash scenarios.

The influence of light level was determined for three pedestrian crash scenarios associated with three adaptive headlighting solutions-curve lighting, motorway lighting, and cornering light. These results were coupled to corresponding prevalence data for each scenario to derive measures of annual lifesaving potential. For each scenario, the risk associated with light level was determined using daylight saving time (DST) transitions to produce a dark/light interval risk ratio; prevalence was determined using the corresponding annual crash rate in darkness for each scenario. For curve lighting, pedestrian crashes on curved roadways were examined; for motorway lighting, crashes associated with high speed roadways were examined; and for cornering light, crashes involving turning vehicles at intersections were examined. In the curve analysis, lower dark/light crash ratios were observed for curved sections of roadway compared to straight roads. In the motorway analysis, posted speed limit was the dominant predictor of this ratio for the fatal crash dataset; road function class was the dominant predictor of the ratio for the fatal/nonfatal dataset. Finally, in the intersection crash analysis, the dark/light ratio for turning vehicles was lower than for nonturning vehicles; and the ratio at intersections was lower than at non-intersections. Relative safety need was determined by combining the dark/light ratio with prevalence data to produce an idealized measure of lifesaving potential. While all three scenarios suggested a potential for safety improvement, scenarios related to high speed roadway environments showed the greatest potential.

Accidents, Traffic↗

PubMed2006

Modeling aggressive driver behavior at unsignalized intersections.

The processing of vehicles at unsignalized intersections is a complex and highly interactive process, whereby each driver makes individual decisions about when, where, and how to complete the required maneuver, subject to his perceptions of distances, velocities, and own car's performance. Typically, the performance of priority-unsignalized intersections has been modeled with probabilistic approaches that consider the distribution of gaps in the major-traffic stream and their acceptance by the drivers of minor street vehicles based on the driver's "critical gap". This paper investigates the aggressive behavior of minor street vehicles at intersections that are priority-unsignalized but operate with little respect of control measures. The objective is to formulate a behavioral model that predicts the probability that a driver performs an aggressive maneuver as a function of a set of driver and traffic attributes. Parameters that were tested and modeled include driver characteristics (gender and age), car characteristics (performance and model year), and traffic attributes (number of rejected gaps, total waiting time at head of queue, and major-traffic speed). Binary probit models are developed and tested, based on a collected data set from an unsignalized intersection in the city of Beirut, to determine which of the studied variables are statistically significant in determining the aggressiveness of a specific driver. Primary conclusions reveal that age, car performance, and average speed on the major road are the major determinants of aggressive behavior. Another striking conclusion is that the total waiting time of the driver while waiting for an acceptable gap is of little significance in incurring the "forcing" behavior. The obtained model is incorporated in a simple simulation framework that reflects driver behavior and traffic stream interactions in estimating delay and conflict measures at unsignalized intersections. The simulation results were then compared against real world observations, representing an important step in validating the model of aggressive driver behavior at unsignalized intersections.

Age Factors↗