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

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

Highway alignment: Three-dimensional problem and three-dimensional solution

Highway geometric design has usually been considered in separate two-dimensional (2-D) projections of horizontal and vertical alignments. Such a practice was followed mainly because three-dimensional (3-D) analysis of combined highway alignments was expected to be difficult. As a result, the effect of ignoring the 3-D nature of the highway alignment could not be quantified. With the long-term objective of developing 3-D design practice, a framework for 3-D highway geometric design was developed and 3-D sight distance was extensively studied as the first design basis. The status of sight distance in current design policies and previous research is summarized, and mainly 2-D analysis was considered. The five main tasks performed to cover the 3-D highway sight distance are presented. (a) As a preliminary step, the 2-D sight distance on complex separate horizontal and vertical alignments was modeled, and the finite element method was used for the first time in the highway geometric design, (b) The 2-D models were then expanded to cover the daytime and nighttime sight distances on 3-D combined alignments. (c) The analytical models were coded into computer software that can determine the available sight distance on actual highway segments. (d) The models were applied in 3-D design of combined horizontal and vertical curves in cut-and-fill sections, and preliminary design aids were derived. (e) Finally, a new concept of red zones was suggested to mark the locations on alignments designed according to current practices where the available sight distance will drop below that required. A comprehensive work on 3-D sight distance analysis has been compiled that should be of great importance for highway researchers and professionals

Analytical model for sight distance analysis on three-dimensional highway alignments

Existing sight distance models are applicable only to two-dimensional (2-D) separate horizontal and vertical alignments or simple elements of these separate alignments (vertical curve, horizontal curve). A new model is presented for determining the available sight distance on 3-D combined horizontal and vertical alignments. The model is based on the curved parametric elements that have been used in the finite element method. The elements presented are rectangular (4-node, 6-node, and 8-node elements) and triangular. These elements are used to represent various features of the highway surface and sight obstructions, including tangents (grades), horizontal curves, vertical curves, traveled lanes, shoulders, side slopes, cross slopes, superelevation, lateral obstructions, and overpasses. The available sight distance is found analytically by examining the intersection between the sight line and the elements representing the highway surface and the sight obstructions. Application of the new model is illustrated using numerical examples, and the results show that existing 2-D models may underestimate or overestimate the available sight distance. The proposed model should be valuable in establishing design standards and guidelines for 3-D highway alignments and determining the effect of various highway features on sight distance