Risk analysis of animal–vehicle crashes: a hierarchical Bayesian approach to spatial modelling

Driving along any rural road within Western Australia involves some level of uncertainty about encountering an animal whether it is wildlife, farm stock or domestic. This level of uncertainty can vary depending on factors such as the surrounding land use, water source, geometry of the road, speed limits and signage. This paper aims to model the risk of animal–vehicle crashes (AVCs) on a segmented highway. A hierarchical Bayesian model involving multivariate Poisson lognormal regression is used in establishing the relationship between AVCs and the contributing factors. Findings of this study show that farming on both sides of a road, a mixture of farming and forest roadside vegetation and roadside vegetation have significant positive effect on AVCs, while speed limits and horizontal curves indicate a negative effect. AVCs consist of both spatial- and segment-specific contributions, even though the spatial random error does not dominate model variability. Segment 15 is identified as the highest risk segment and its nearby segments also exhibit high risk

Super performance of AMIR compactor in Australia

Construction-induced cracks have been analyzed and explained using the equation of relative rigidity. It has been shown that conventional rolling equipment are the main causes of the se cracks. The analytical results were validateded by laboratory simulation and field observations. These results led to the design and manufacture of a number of laboratory models and full-scale new compactors, called Asphalt Multi-Integrated Roller (AMIR). The AMIR' compactor has an infinite radius and a soft interface with the asphalt mix during compaction. An Australian company used AMIR and a combination of vibratory and pneumatic rollers, side by side, to compact a sand layer and two asphalt sections with two different mixes in Sydney. The Australian results, which showed super performance by AMIR, have verified the results of a number of Canadian field trials carried out in the 1990s. Consequently, the Australian company modified AMIR to enhance its mechanical features and developed an advanced compactor. This paper presents the Australian field trials, including field observations and the results of laboratory tests performed on cores and beams recovered from the field. A comparison between the main results of the Australian and Canadian field trials is also presented. The results of this paper confirm the superior performance of AMIR over conventional rollers, and therefore should be of interest to the pavement industry

Vehicle stability on combined horizontal and vertical alignments

Computer simulation was used in this study to examine vehicle stability through lateral acceleration levels. The objective was to compare the minimum flat horizontal curve radius used in traditional geometric design guides with the minimum radius based on vehicle dynamics on three-dimensional (3D) alignments. A vehicle dynamics simulation computer program was used to examine vehicle dynamics and stability on 3D alignments. The program uses a sophisticated two-axle dynamics model that traditionally has only been used by mechanical engineers in experimenting with vehicle characteristics. It was found that vehicle stability is not compromised on 3D alignments compared to 2D alignments for the test cases examined. However, differences in the required minimum horizontal radii were obtained due to the transient effects of a vehicle traveling along a horizontal curve. These transient effects, due to changes in road geometry, include driver steering, vehicle off tracking, and vehicle roll. In order to maintain currently acceptable comfort threshold, increases in the order of 3-16% in the minimum horizontal radii suggested by the current North American geometric design guides are required

Low-temperature stresses and fracture analysis of asphalt overlays

Thermal cracking of asphalt overlays is a leading cause of pavement deterioration. The thermoelastic response of a multilayered pavement structure is modeled using a transient thermal analysis followed by a quasi-static stress analysis at discrete time intervals using finite element analysis. Numerical analysis of two- and three-dimensional cracking problems is performed. Based on a fracture mechanics approach, the potential of thermal cracks to propagate through the overlay is examined using both a displacement formula and an energy-balance principle. The interaction between multiple cracks and the effect of bond between layers on crack propagation are examined. The proposed numerical methods for analysis of pavement thermal cracking provide a means to characterize and optimize different evolving materials and innovative pavement reinforcement techniques

Sight distance evaluation on complex highway vertical alignments

Sight distance (stopping, passing, and decision) is a key element in highway geometric design. Existing models for evaluating sight distance on vertical alignments are applicable only to simple, isolated elements such as a crest vertical curve, a sag vertical curve, and a reverse vertical curve (a sag curve following a crest curve, or vice versa). This paper presents an analytical methodology for evaluating sight distance on complex vertical alignments that involve any combination of vertical alignment elements. The methodology can be used for evaluating passing sight distance on two-lane highways, and stopping sight distance and decision sight distance on all highways. Sight distance controlled by the headlight beam can also be evaluated. The locations of sight-hidden dips, which may develop when a sag vertical curve follows a crest vertical curve with or without a common tangent, can be determined. Also, sight distances obstructed by overpasses are evaluated. A profile of the available sight distance can be established and used to evaluate sight distance deficiency and the effect of alignment improvements. A software was developed and can be used for determining the available sight distance accurately. The software may replace the current field and graphical practice for establishing the no-passing zones and evaluating stopping and decision sight distances on complex vertical alignments

Automation of determining passing and no-passing zones on two-lane highways

Establishing passing and no-passing zones has been a major task for highway agencies to ensure that neither safety nor highway capacity is compromised. Currently, no-passing zones are established using a graphical technique, based on two-dimensional (2-D) horizontal and vertical alignments, and (or) field measurements. As a result, this task has been time consuming, expensive, and subject to human errors. Moreover, decisions are taken by the field crew, and designers do not have flexibility to change the alignment and check the corresponding effect on passing zones. This article reviews analytical models developed by the authors for sight distance analysis on 2-D and 3-D highway alignments. Based on these models, two computer programs, MARKS and MARKC, are developed to determine the sight distance on 2-D separate and 3-D combined alignments, respectively. MARKS was verified graphically, and MARKC was verified using field measurements. The verification showed that the two programs can determine the available sight distance accurately. The implementation of the developed software has the potential benefits of eliminating human errors, saving time and cost, providing greater flexibility to designers to change the alignment and easily check the effect on passing zones, and transferring the decision of allowing or disallowing passing from field crews to engineers

Passing sight distance on two-lane highways: Review and revision

Several models have been developed to determine the minimum passing sight distance required for safe and efficient operation on two-lane highways. The American Association of State Highway and Transportation Officials has developed a model assuming that once the driver begins a pass, he/she has no opportunity but to complete it. This assumption is believed to result in exaggerated passing sight distance requirements. Considerably shorter passing sight distance values are presented in the Manual of Uniform Traffic Control Devices and are used as the marking standards in Canada and the U.S.A. More appropriate models have been developed considering the driver's opportunity to abort the pass, and are based on a critical sight distance which produces the same factor of safety whether the pass is completed or aborted. However, these models need to be revised to determine the passing sight distance requirements more accurately and to closely match field observations. In this paper, a revised model for determining the minimum required passing sight distance was developed, based on the concept of critical sight distance and considering the kinematic interaction between the passing, passed, and opposing vehicles. The results of the revised model were compared with field data and showed that the revised model simulates the passing manoeuvre better than the currently-available models which are either too conservative or too liberal. The results showed that the passing sight distance requirements recommended in the Manual of Uniform Traffic Control Devices are sufficient at low design speeds (50-60 k.p.h.) and for manoeuvres involving passenger cars only. For higher design speeds, the Manual of Uniform Traffic Control Devices standards are less than the passing sight distance required for safe and comfortable passes. The deficiency was found to increase with the increase in design speed, and reaches about 36% at a 120-k.p.h. design speed. Based on these results, major revisions to the current Manual of Uniform Traffic Control Devices mark