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The research addresses the acceleration impact on vehicle safety during tractive mode for control road geometry parameters and vehicle speeds at and below the suggested relevant design speed values. Instrumented field measurements on speed distance data and pavement friction supply were collected utilizing a FWD C-Class passenger car and correlated against an existing dynamic model in order to examine the interaction between vehicle dynamics and road geometry. Aiming to quantify the potential safety hazard during vehicle acceleration at impending skid conditions on curves, the analysis revealed that the conventional approach of addressing vehicle safety based on posted speed management seems inadequate. Even when the speed of the vehicle is less than the relevant posted value, the acceleration effect which depends on the utilized horsepower rates may result in vehicle skidding. Among other important findings, stands also the necessity for monitoring friction supply as well as the fact that vehicles equipped with excessive amounts of horsepower rates must be driven very conservatively, especially on sharp curves combined with poor friction supply. The authors believe that besides data on speed, pavement friction and road geometry, the provision of additional information on vehicle horsepower utilization, incorporated in a more sophisticated intelligent speed adaption (ISA) process of vehicle advanced driver assistance systems (ADAS) in the near future, will deliver integrated and more comprehensive, in terms of safety, guidance to drivers. [ABSTRACT FROM AUTHOR]

The objective of this paper is to create or establish a suitable methodology that exploits the geometric features that characterize the existing infrastructure on two-lane rural highways, regarding the geometric features (horizontal and vertical alignment, superelevation, sight distance) and evaluating the provided road safety level. Through the utilization of these elements, the purpose is the determination of evaluation coefficients that show the hazard level of every road section and the critical regions of the road network, while identifying the crucial curves which have high potential for road accidents. In this context, a hierarchy of critical parameters influencing the hazard rating of a road network was made regarding to geometric design. For each of these parameters, appropriate mathematical rating equations were created, based on the limit values presented in the literature. Initially, each parameter was correlated with the limits set by the geometric design guidelines, while simultaneously the hazard level and the sensitivity of each parameter were defined. By this procedure, appropriate mathematical expressions that estimate the hazard level were developed, and also appropriate weighing coefficients were sought. Thus, a combined rating that characterizes each road section was obtained and the critical curves that present high possibility of accident occurrence were depicted. Finally, data was collected for a significant sample, of about 1000km, of the existing Greek road network in order both the results of the proposed methodology to be evaluated and also these to be compared with the results of the operating speeds Vss of two consecutive and independent geometrical elements of the road. [ABSTRACT FROM AUTHOR]

Crash data in the USA show that approximately 47 percent of fatal crashes occur at night. Sight distance is severely reduced at nighttime as it compares to that in the day often resulting in problematic situations. Horizontal alignment can compound this issue, since most drivers would not be able to see far in advance to recognize the sharpness of the curve and adjust their speed accordingly: a process that they can complete at daylight conditions. This study attempts to understand the influence of roadway geometry and especially curvature on nighttime crashes and presents a preliminary analysis of this issue aiming to identify the magnitude of the problem and provide some guidance for future research. The findings indicate that there is indeed an increased crash occurrence at night and this is related to the curve radius. Sharper curves, i.e., curves with small radii, showed an increase in crashes and crash rate when they were compared to their corresponding daytime crashes. Design consistency was also examined by considering the radii of successive curves. The data again points to the differences in crash experience when considering the relation between two successive curves. Additional work is needed to further explore these issues and develop more statistically robust models for refining the nomographs developed here. [ABSTRACT FROM AUTHOR]

The objective of this paper is to develop a mathematical methodology that allows the available sight distance calculation of a roadway directly in three-dimensional space and in a fully automatic and accurate manner. The presented methodology overcomes the conventional approach of studying the three-dimensional roadway configuration separately and sequentially in its horizontal and vertical alignment. As far as the road surface is concerned, it is simulated as a 3-d B-spline surface with continuous side barriers whose road centerline has been in turn, simulated as a 3-d B-spline curve. Through this approximation, the road centerline as well as the right and left borderlines which play a crucial role in the sight distance calculation are mathematically defined both geometrically and analytically. The sight distance calculation can be made in each point of the road surface, due to the integrated information existing in the model through its three-dimensional character. These calculations are clearly more reliable, since they are applied on a realistic 3-d road surface. It is worth mentioning that this methodology can be applied on existing roads as well as during the design process by modifying the pseudogeodesic and/or pseudonormal curvature of the roadway in order to obtain the desired available sight distance. Finally, the computational part of this methodology is attained by expressing all the functions and algorithms in code through the programming language offered by the software Mathematica, whereas the whole process is demonstrated as a case study accompanied by Figures and Tables. [ABSTRACT FROM AUTHOR]

Stopping Sight Distance (SSD) is a key control element which directly affects the suggested values of crucial road design parameters. Although there is a significant difference in SSD values between upgrades and downgrades, many Design Policies ignore the grade effect during vehicle braking on variable grades. Such a case is experienced during the determination of sag vertical curvature rates where the relevant SSD values are extracted assuming leveled road geometry. The paper investigates possible deficiency of this approach, regarding cases where the length of the vertical curve exceeds the control SSD values. The authors addressed the SSD calculation on variable grades during the braking process through a recently developed process that relates the point mass model and the laws of mechanics. For a wide range of design speed values, charts illustrating the required SSDs were drawn as a function of negative entering grade values related to control sag vertical curve rates, as adopted by AASHTO. The process revealed numerous SSD shortage areas, where the authors provided revised sag vertical curvature rates, in order to grant SSD adequacy throughout the vehicles' breaking process. Furthermore, the authors aiming to provide the designers with ready-to-use vertical design tool associated the amended vertical curvature rates to AASHTO's road functional classification, as a function of the sag vertical curve's entering grade value. [ABSTRACT FROM AUTHOR]

Highway Geometric Design criteria are based primarily on daytime driving conditions ignoring nighttime driving. The present paper aims at filling part of this existing gap by presenting an analysis on the Available Sight Distance (ASD) at night and its relationship to horizontal geometric design on dry pavements of two-lane rural roads. The sight distance analysis was based on the Relative Visual Performance model (RVP) and covers all three groups of the driving population; young, middle-aged and older drivers. Two different vehicle headlamps (High Intensity Discharge-Xenon and Tungsten-Halogen) were taken into account compared the drivers' ability to identify a possible obstacle. As obstacles were used two common wildlife animals, which present real-life hazards caused, increased rates of mortalities on roadways in U.S.A. and Greece, at night. Namely these are the white-tailed deer (Odocoileus virginianus) and the domestic goat (Capra aegagrus hircus) respectively. In the present study an effort has been made to approach the worst luminance driving scenario by presenting the minimum safety levels of driver's visibility at nighttime. [ABSTRACT FROM AUTHOR]

In current road design practice still a 2D approach is in use both with respect to the road configuration and the vehicle's motion, despite the fact that a 3D approach regarding these aspects is the only accurate and realistic method to control the provision of critical design parameters such as the adequacy of Stopping Sight Distances (SSD). This paper describes an accurate SSD control method that relates the 3D configuration of a roadway to the dynamics of a vehicle moving along the actual roadway path, based on the difference between the provided and the demanded SSD. The SSDDEMAND is defined from the mass point model adopted by AASHTO enriched by the actual values of grade and friction variation. On the other hand the SSDPROVIDED is described as the 3D driver's line of sight towards the object height. From this method the conditions of SSD provision could be derived for a variety of 3D alignment combinations and a wide range of design speeds and compared with the design elements' limiting values as suggested by the AASHTO 2004 design guidelines. The relevant investigation revealed a satisfactory SSD reserve only in cases of horizontal curved alignments overlapped with vertical curves. The analysis showed that, in order to ensure SSD adequacy on road alignments designed according to the AASHTO design guidelines, a slight increase of the AASHTO minimum values for Crest Vertical Curvature Rates is necessary. The SSD control methodology presented in the paper is suitable for SSD evaluation regarding both existing and new road sections. [ABSTRACT FROM AUTHOR]

Current geometric design policies use passenger cars as design vehicles, while truck operational and dynamic characteristics are not included or not addressed consistently. Furthermore, critical geometric design parameters such as horizontal curves radii are determined without consideration of the effect of vertical alignment. The objective of this work is to investigate whether critical road sections such as reverse horizontal curves with spiral curves, can accommodate typical heavy vehicles with safety. The analysis was focused on rural and suburban two-lane roads with undivided pavement that produce the largest accident rates. By means of "road - driver - vehicle" simulation system developed in TruckSim, the vehicle dynamic response to inputs from the immediate environment is analyzed, while same kind of outputs that might be measured with physical tests involving instrumented vehicles are calculated and plotted. Results indicated that horizontal curves minimum radii that are implemented according to several design criteria, can not be used in conjunction with the allowed interval of grades, and that the table of minimum radii must comprehend a limitation for the applicable grade. Otherwise, exclusively speed limits depending on the road geometry or larger radii must be used in order to adequately accommodate heavy vehicles. [ABSTRACT FROM AUTHOR]