Advances in Regression Kriging-Based Methods for Estimating Statewide Winter Weather Collisions: An Empirical Investigation

Winter conditions create hazardous roads that municipalities work hard to maintain to ensure the safety of the travelling public. Targeting their efforts with effective network screening will help transportation managers address these problems. In our recent efforts, regression kriging was found to be a viable and effective network screening methodology. However, the study was constrained by its limited spatial extent making the reported results less conclusive and transferrable. In addition, our previous work implemented what has long been adopted in most of conventional studies—the Euclidean distance; however, use of the road network distance would, intuitively, result in further improving kriging estimates, especially when dealing with transportation problems. Therefore, this study improves upon our previous efforts by developing a more advanced kriging model; namely, network regression kriging using the entire state of Iowa with the significantly expanded road network. The transferability of the developed models is also explored to investigate its generalization potential. The findings based on various statistical measures suggest that the enhanced kriging model vastly improved the estimation performance at the cost of greater computational complexity and run times. The study also suggests that regional semivariograms better represent the true nature of the local variances, though an overall model may still function adequately if higher fidelity is not required.

Network Screening Methods to Identify Roadway Sites for Safety Investigation: An Examination of Some Critical Issues

Traffic accidents are responsible for about 3,000 deaths and $25 billion in economic losses annually in Canada. One way for transportation authorities to improve safety is to identify potentially hazardous roadway elements through network screening. The process of network screening is a low-cost statistical analysis of highway safety data, which yields a ranked list of sites to be investigated in detail. Critical issues of two network screening methods are investigated in this thesis. The first method is a peak-searching algorithm for screening roadway segments, with attention focused on threshold values of a key user-selected variable, namely the coefficient of variation. The second method examined is a method of screening for high proportions of specific accident types. For this method, parameter estimation techniques are compared, and the effect of the 'critical proportion,' a key user-selected variable in the method, on site rankings is investigated. In addition to the two network screening methods, an investigation is carried out into some aspects of safety performance function calibrated using negative binomial regression. Specific attention is given to how the negative binomial dispension parameter changes over the range of some independent variables.

Network screening for specific collision types at urban signalized intersections - conventional and spatial methods

Transportation authorities are always looking for ways to improve road safety since vehicle collisions cost Canada 25 billion dollars of capital loss and around 2800 deaths each year. An important step in improving road safety is to sieve out the problem sites through network screening processes. screening for specific accident types is discussed in this thesis, using signalized intersections in Toronto in an illustrative application. each such collision type is associated with corresponding countermeasures, which allows the engineer to rank the entities with specific remedies in mind. In this way, the effectiveness of road network screening can improved through targeted treatments. Three different screening methods are introduced and compared; procedures for selecting entities from screening results by different methods are also presented. A process for ranking jurisdictions by regions is proposed. This is a method which combines the conventional network screening techniques with geographic information system (GIS) tools. The GIS can integrate the spatial information of a selected area with the conventional accident and road characteristic data and facilitate network screening by region.

Network screening for specific collision types at urban signalized intersections - conventional and spatial methods

Transportation authorities are always looking for ways to improve road safety since vehicle collisions cost Canada 25 billion dollars of capital loss and around 2800 deaths each year. An important step in improving road safety is to sieve out the problem sites through network screening processes. screening for specific accident types is discussed in this thesis, using signalized intersections in Toronto in an illustrative application. each such collision type is associated with corresponding countermeasures, which allows the engineer to rank the entities with specific remedies in mind. In this way, the effectiveness of road network screening can improved through targeted treatments. Three different screening methods are introduced and compared; procedures for selecting entities from screening results by different methods are also presented. A process for ranking jurisdictions by regions is proposed. This is a method which combines the conventional network screening techniques with geographic information system (GIS) tools. The GIS can integrate the spatial information of a selected area with the conventional accident and road characteristic data and facilitate network screening by region.

Network Screening Methods to Identify Roadway Sites for Safety Investigation: An Examination of Some Critical Issues

Traffic accidents are responsible for about 3,000 deaths and $25 billion in economic losses annually in Canada. One way for transportation authorities to improve safety is to identify potentially hazardous roadway elements through network screening. The process of network screening is a low-cost statistical analysis of highway safety data, which yields a ranked list of sites to be investigated in detail. Critical issues of two network screening methods are investigated in this thesis. The first method is a peak-searching algorithm for screening roadway segments, with attention focused on threshold values of a key user-selected variable, namely the coefficient of variation. The second method examined is a method of screening for high proportions of specific accident types. For this method, parameter estimation techniques are compared, and the effect of the 'critical proportion,' a key user-selected variable in the method, on site rankings is investigated. In addition to the two network screening methods, an investigation is carried out into some aspects of safety performance function calibrated using negative binomial regression. Specific attention is given to how the negative binomial dispension parameter changes over the range of some independent variables.

Safety performance assessment of freeway interchanges, ramps and ramp terminals

Existing safety performance functions for mainline interchanges and ramps of Ontario freeways are updated using negative binomial regression. The functional forms of the updated models are different from the existing models. In addition, new safety performance functions for ramp terminal sites are developed. Network screening to identify sites in need of safety treatment has been illustrated using two different methods, one based on a potential for safety improvement (PSI) index and, the other based on an index of a high proportion of a specific accident type. A comparison for rankings for 3-legged signalized ramp terminals by the two methods indicates reasonably consistent results, with some key differences. The method of screening for high proportion of specific accidents can be a possible alternative to PSI index method where safety performance functions and/or traffic volumes are not available since, unlike the PSI Index method, it does not require these inputs.

Safety performance assessment of freeway interchanges, ramps and ramp terminals

Existing safety performance functions for mainline interchanges and ramps of Ontario freeways are updated using negative binomial regression. The functional forms of the updated models are different from the existing models. In addition, new safety performance functions for ramp terminal sites are developed. Network screening to identify sites in need of safety treatment has been illustrated using two different methods, one based on a potential for safety improvement (PSI) index and, the other based on an index of a high proportion of a specific accident type. A comparison for rankings for 3-legged signalized ramp terminals by the two methods indicates reasonably consistent results, with some key differences. The method of screening for high proportion of specific accidents can be a possible alternative to PSI index method where safety performance functions and/or traffic volumes are not available since, unlike the PSI Index method, it does not require these inputs.