Search

In 2014, highway vehicles accounted for 72.8% of all Greenhouse Gases emissions from transportation in Europe. In the United States (US), emissions follow a similar trend. Although many initiatives try to mitigate emissions by focusing on traffic operations, little is known about the relationship between emissions and road design. It is feasible that some designs may increase average flow speed and reduce accelerations, consequently minimizing emissions. This study aims to evaluate the impact of road horizontal alignment on CO 2 emissions produced by passenger cars using a new methodology based on naturalistic data collection. Individual continuous speed profiles were collected from actual drivers along eleven two-lane rural road sections that were divided into 29 homogeneous road segments. The CO 2 emission rate for each homogeneous road segment was estimated as the average of CO 2 emission rates of all vehicles driving, estimated by applying the VT-Micro model. The analysis concluded that CO 2 emission rates increase with the Curvature Change Rate. Smooth road segments normally allowed drivers to reach higher speeds and maintain them with fewer accelerations. Additionally, smother segments required less time to cover the same distance, so emissions per length were lower. It was also observed that low mean speeds produce high CO 2 emission rates and they increase even more on roads with high speed dispersions. Based on this data, several regression models were calibrated for different vehicle types to estimate CO 2 emissions on a specific road segment. These results could be used to incorporate sustainability principles to highway geometric design. [ABSTRACT FROM AUTHOR]

Abstract: Highway geometric design in mountainous areas has been a typical challenge. The combination of short horizontal curves and restricted right-of-way is a common ground for contemplating design exception in British Columbia, Canada. In practice, collision modification factors (CMFs) are advocated as quantitative measures of changes in road features on safety. However, in many situations, there are no CMFs in the literature to predict the safety impact of changing particular road features. An important example of these road features is sight distance restriction on horizontal curves. A mechanism for risk measurement has been proposed in earlier work to assist designers in comparing the safety impact of different deviations from sight distance requirements. This paper attempts to answer the questions as to whether it is possible to reduce overall risk and achieve consistency in such reduction without demanding wider right-of-way. This problem was formulated in a multi-objective optimization framework. Following this methodology, it was possible to achieve an average reduction in risk of 25% on the nine critical cross-sections. This reduction in risk was achieved without demanding wider right-of-way and without creating measurable increase in expected collision frequency due to independent re-dimensioning of different geometric elements. On theoretical grounds, this paper represents another step into the direction of developing fully probabilistic geometric design standards. On practical grounds, this paper provides an important decision mechanism that enables the efficient use of available right-of-way for new highway construction. Case studies in this paper have been applied on a major highway development in British Columba, Canada. [Copyright &y& Elsevier]

The development of highway standard design models involves various assumptions regarding design inputs and the road environment. This paper suggests an improvement to the treatment of uncertainty in design inputs by replacing the current deterministic approach with a reliability-based framework. Reliability theory deals with the propagation of quantified variability in design inputs throughout the design process. In such a framework, each design output corresponds to a theoretical probability of noncompliance to design requirements. These probabilities can be used to assess and compare the a priori safety level associated with various design scenarios. This paper proposes that such a priori safety level of standard design outputs should be consistent and close to a prespecified target level. A set of methods is proposed to determine a target value for design safety. A general framework for calibrating standard design models is presented. To demonstrate the concept, the paper presents an application of the calibration framework to the standard design model of crest vertical curves. Calibrated design charts are constructed to yield a consistent design safety level. [ABSTRACT FROM AUTHOR]

In current design guides, the minimum radii of compound horizontal curves are based on the design requirements of simple horizontal curves for each arc on flat terrain. Such a design ignores the effects of compound curvature and vertical alignment. This paper uses computer simulation software to establish the minimum radius requirements for compound curves, considering these effects. The actual lateral acceleration experienced by a vehicle negotiating a two-dimensional (2-D) simple curve is recorded as a base scenario to facilitate the analysis of a compound curve on a flat terrain or combined with vertical alignment (three-dimensional (3-D) compound curves). The vertical alignments examined include upgrades, downgrades, crest curves, and sag curves. Mathematical models for minimum radius requirements were developed for flat and 3-D compound curves. Three types of design vehicles were used. The results show that an increase in the minimum radius ranging from 5% to 26% is required to compensate for the effects of both compound curvature and vertical alignment. [ABSTRACT FROM AUTHOR]

Many models have been developed to evaluate the operating speeds on two-lane rural highways. However, provided information usually lacks details essential to assess their applicability at locations other than where they were developed. This paper presents a procedure to interpret raw data collected on three horizontal curve sites of different two-lane rural highway classes in Ontario. The speed observations were categorized into three vehicle classes (passenger car, light truck, and multi-axle heavy truck) and four light condition categories (day, night, and two transition periods). The minimum headway and percentile value to define the operating speed were examined, and a revision of the current practice deemed not warranted. The findings also indicated that operating speeds do not depend on the time or vehicle class. Finally, the horizontal alignment affects the operating speed, but the speeds of the two travel directions on a horizontal curve may differ even with little contribution of the vertical alignment. [ABSTRACT FROM AUTHOR]

Highway geometric design is a complex process that is closely related to human perception and behaviour. Among the human perception issues that can affect highway geometric design is the preview sight distance, which has been defined as the distance required to perceive a horizontal curve and react properly to it. Previous attempts to quantify preview sight distance included measurement on actual roads, physical modelling, and computer animation. This paper presents a computer animation experiment that was designed to examine the effects of geometric parameters and driver characteristics on preview sight distance and to statistically model preview sight distance. Statistical analysis showed that preview sight distance depends on geometric parameters such as the horizontal curve radius, use of spiral curve and its length, presence of crest vertical curve, algebraic difference of vertical grades, vertical curvature, and road delineation. On the other hand, driver characteristics were mostly found to be insignificant parameters. Finally, statistical models were developed to predict the value of preview sight distance using linear regression analysis. The models vary in simplicity and accuracy and were formulated as a function of the general alignment configuration or as a function of the exact geometric parameters.Key words: highway geometric design, sight distance, driver characteristics, three-dimensional alignment.La conception de la géométrie d'une autoroute est un processus complexe qui est relié étroitement à la perception et au comportement humain. Parmi les sujets de perception humaine qui peuvent affecter la conception de la géométrie d'une autoroute est la distance de réaction, qui est définie comme la distance requise pour percevoir une courbe horizontale et réagir en conséquence. Les essais précédents afin de quantifier la distance de réaction ont inclus des mesures sur des routes réelles, la modélisation physique et l'animation par ordinateur. Cet article présente une expérimentation avec animations par ordinateur, qui a été conçue pour examiner les effets de paramètres géométriques et de caractéristiques propres aux conducteurs sur la distance de réaction et pour modéliser statistiquement la distance de réaction. Les analyses statistiques ont montré que la distance de réaction dépend des paramètres géometriques, tels que le rayon de la courbe horizontale, l'utilisation de courbes en spirale et leur longueur, la présence d'une courbe verticale avec une crête, la différence algébrique entre des grades verticaux, la courbure verticale, et l'alignement de la route. D'autre part, il a été trouvé que les caractéristiques des conducteurs sont des paramètres non significatifs. Finalement, des modèles statistiques ont été developpés afin de prédire la valeur de la distance de réaction en utilisant une analyse de régression linéaire. Les modèles varient en termes de simplicité et de précision, et ont été formulés en fonction de la configuration de l'alignement général ou en fonction des paramètres géométriques exacts.Mots clés : conception de la géométrie d'une autoroute, distance de vue, caractéristiques des conducteurs, alignement en trois dimensions.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]