Many researches have proved that one of the parameters that most influence the safe driving is the operating speed defined as the speed at which drivers travel on a dry road in free flow conditions during daylight hours. This study describes a comparison between the driver speed behavior on horizontal circular curves located in Serbia and the driver speed behavior on circular curves located in Italy with analogous infrastructural-geometric contexts. Only curves falling within two-lane rural roads network in low-volume conditions without spiral transition curves have been studied. Operating speed profiles were plotted and a careful analysis was carried out to study the deceleration/acceleration motion at each selected curve. Speed measurements were conducted by using different devices: a) for Italian case, laser detectors were used that emit and receive a pair of laser beams perpendicularly to the road’s axis and they record the instantaneous vehicle speed; b) for Serbian case, sensors were used with an applicant software developed in the LabVIEW programming environment and signals logged in a binary file for which the vehicle speed is measured on basis of the passing time between two consecutive sensors along the curve. Two driver behavior types were found: a) drivers that decelerate approaching the middle of the curve and accelerate leaving it; b) drivers that decelerate on the whole circular curve length. T-test was performed. Statistically, no significant difference was produced from the analysis when circular curves are located in different states which reflect the same geometric, traffic and environmental context

New Serbian policies on road design introduce the concept of operating speeds. Decades ago, national policies were based on the constant design speed concept. Among other design parameters, in relation to that constant design speed, minimum radii of horizontal and vertical road geometry were determined. Introduction of the operating speed concept provides for more realistic prediction of speed levels along the road. Unlike the constant design speed, operating speed levels vary along the road, reaching higher levels in curves with larger radii, on straight sections and on reverse curves and dropping down to the design speed level in horizontal curves with the minimum radius. Consequently, besides a constant Stopping Sight Distance (SSD), which is calculated from the constant design speed, the new term, Required Sight Distance (RSD) is introduced. RSD varies along the road, as it is calculated from the operating speed, which also varies along the road. Appropriate RSD analyses are crucial on road rehabilitation projects, since a simple resurfacing that enables higher speed levels, without providing increased RSD, may hamper the safety of a newly resurfaced road. Software tools for predicting operating speed levels and optical analyses of the road are also presented in this paper. Software tools for RSD analyses enable the import of lines of sight into the 3D model of the roadway and their export into the cross sections extracted from the model, thus facilitating the obstacle removal. Also demonstrated are tools for determining Available Sight Distance (ASD), which are based on triangulated 3D models of the roadway as well.

Exits on multilevel interchange ramps present potentially dangerous spots from the point of traffic safety. Therefore, a range of vehicle restraint systems was developed to reduce the consequences of traffic accidents. Proper installation of adequate crash cushion systems requires sufficient space (length) at the point where the ramp leaves major road. To provide for an installation of such a system, the basic geometry of the exit ramp must be reconsidered, introducing the appropriate ration between the radius and transition curve.

Tunnel fire safety plays a key role in the railway operations and many procedural and\ud technological improvements have been realized in order to prevent and mitigate the fire risk. The fire\ud prevention and protection procedures can be approached through two main different strategies: the deterministic/\ud prescriptive based approach and the performance-based approach. In the study presented in this\ud paper, the possibility of application of the water curtain-based wayside fire protection system, as one of\ud the auxiliary systems for improving and upgrading the fire safety in the railway tunnels for the smoke\ud compartmentation, has been studied and analysed. A finite element-based dynamic simulation model has\ud been developed in order to simulate different fire scenarios and to assess the water curtain-based fire protection\ud system performances in terms of efficiency against the toxic smokes and gases propagation into\ud the railway tunnel. Some preliminary numerical results have been presente

Median represents a portion of an urban road separating opposing directions of the traveled way. Due to their function to provide enough space for separate traffic lane and storage of left-turning vehicles, the medians are highly desirable on city arteries carrying two or more lanes per travel direction. Type and dimensions of turning vehicles significantly affect the design of a median openings and median ends. The design solution and the geometry of median ends should be based on the composition of all left-turning movements occurring simultaneously at at-grade intersection. After selection of design vehicles for swept path analysis of the characteristic turning maneuvers in intersection, larger vehicles should be further checked for their ability to turn without undue encroachment on adjacent traffic lanes. The critical design parameter is the median width, especially at the ends of the median openings. Dragging paths of left-turning vehicles shape the median ends geometry. In traditional design practice established in Europe, three-centered compound curves with radii rations R1 : R2 : R3 = 2 : 1 : 3 and R1 : R2 : R3 = 2.5 : 1 : 5.5 are used to approximate dragging pahs of turning vehicles. In this paper, considering the median width, the deficiencies of the traditional design approach are revealed and new findings regarding the design of the median ends at at-grade intersections are presented.