An Integrated 3D Safety-based Approach for the Design of Horizontal Curves using Reliability  Analysis and LiDAR Data
Creators: Mohamed, Amr AS
Publisher: name: University of Alberta Library
Year: 2022

<p>Safety-based design can be described as an approach in which safety is considered a core design input and the safety performance of proposed designs that follow this approach can be expected. Although current-day highway design guidelines are constantly updated to incorporate recent advances in research, there are still several limitations associated with the current design approach. Perhaps the biggest drawback is that the safety levels built into existing guidelines are largely unknown and safety is not explicitly considered as a design input. There is little to no knowledge about the safety implications of deviating from standard requirements. Moreover, current guides do not account for the stochastic nature of design inputs. Design inputs are therefore represented by deterministic values assuming near worst-case scenarios to determine design values leading to uneconomic designs in many cases. There is no information in design guidelines on whether a road designed to meet the minimum requirements of guidelines is capable of accommodating or exceeding driver demand, resulting in uneconomic design in many cases. To address these limitations, many design experts have promoted using reliability analysis as a robust methodology to quantify the risk (known as the probability of non-compliance, Pnc) that a certain design would fail to meet the requirements of the road user demand. <br>
The majority of previous studies on reliability-based highway design focused on assessing the risk associated with horizontal curves considering only one criterion of non-compliance which is insufficient sight distance using 2D sight distance calculations. In fact, this does not represent the nature of the driving environment as non-compliance on curves could result from multiple non-compliance modes such as restricted sight distance and vehicle skidding. Also, sight distance can be restricted by 3D obstructions or the combination of horizontal and vertical alignments which makes using a multimode, also known as a system, reliability analysis and 3D sight distance evaluation more realistic. More so, only a handful of studies established a link between Pnc and collisions. Therefore, establishing a link between the Pnc and safety utilizing 3D sight distance and multi-mode reliability analysis remains unexplored.<br>
To address these limitations, this thesis adopts a safety-based design approach whereby relationships between driver capabilities, curve geometric attributes, and collisions are established. The thesis calibrates safety-based design charts for horizontal curves considering a system reliability analysis where the non-compliance could result from limited sight distance and vehicle skidding. To enable a robust and large-scale reliability analysis, the first phase of the thesis develops novel algorithms that facilitate curve detection and automatic extraction of curve geometric attributes on highways using mobile Light Detection and Ranging (LiDAR) data. Using this approach, curve attributes were collected, and the Available Sight Distance (ASD) was assessed in a 3D environment on 244 horizontal curves in Alberta, Canada. Monte Carlo Simulation was then used to calculate the associated risk levels, and full-Bayes multivariate Poisson lognormal regression was utilized to develop statistically significant safety performance functions that link Pnc to collisions. Safety-based design charts were then calibrated to relate curve attributes to risk levels and expected collision frequency. Structural Equation Modelling (SEM) was also used to study the interaction between curve attributes, Pnc, and collision frequency. The results of SEM presented curve features that directly affect Pnc, safety, and those who have an indirect influence on collisions, which was mediated through Pnc.<br>
The results showed that there is a statistically significant relationship between 𝑃𝑛𝑐 and safety, indicating that higher Pnc rates are associated with higher expected crashes. The calibrated charts showed the importance of using multi-mode reliability analysis, especially on curves with sharp radii where the difference between Pnc of a single-mode and Pnc of a multimode is considerable. An example of using the calibrated charts in estimating the expected safety benefits of geometric improvements was introduced. Guidance to practitioners on using the proposed charts was also provided. The developed charts are ready to use by designers and can offer practitioners a tool to estimate the safety consequences of design alternatives and aid the decision-making process of rehabilitation projects. In summary, the research presented in this dissertation is a step forward towards adopting a safety-based design of highways and is of crucial importance from both theory and practical perspectives. </p>