Information on pavement layer thickness is very important for determining bearing capacity, estimating remaining life and strengthening planning. Ground-penetrating radar (GPR) is a nondestructive testing (NDT) method used for determining the continuous pavement layer thickness in the travel direction. The data obtained with GPR in one survey line is suitable for the needs of repair and rehabilitation planning of roads and highways, but not for wider traffic areas such as airfield pavements. Spatial representation of pavement thickness is more useful for airfield pavements but requires a 3D model. In the absence of 3D GPR, a 3D model of pavement thickness can be created by additional processing of GPR data obtained from multiple survey lines. Five 3D models of asphalt pavements were created to determine how different numbers of survey lines affect their accuracy. The distance between survey lines ranges from 1 to 5 m. The accuracy of the 3D models is determined by comparing the asphalt layer thickness on the model with the values measured on 22 cores. The results, as expected, show that the highest accuracy is achieved for the 3D model created with a distance of 1 m between survey lines, with an average relative error of up to 1.5%. The lowest accuracy was obtained for the 3D model created with a distance of 4 m between the survey lines, with an average relative error of 7.4%.

The design and possible simplifications of four-leg channelized intersections are analysed in the paper. The research resulted in a new simpler approach in which all intersection elements are properly formed from the very beginning, so that the need for the swept path analysis and redefining of intersection elements is rendered superfluous. New procedures for the design of four-leg channelized intersections for the 60 to 90 degree intersection angles, and for semi-trailer trucks 16.5 m in length, are presented.

The roundabout design procedures specified in current standards and guidelines presuppose that the centrelines of the approach legs intersect at right angles at the geometric centre of the roundabout. In urban areas, this requirement cannot always be met due to fixed structural constraints along the approaches. Here, a lateral or radial offset of the approach legs from the roundabout’s geometric centre is required. This offset plays an important role in roundabout design, as it affects the roundabout’s ability to control vehicle speed. This study investigates the effects of a lateral approach leg offset on the geometric design of urban single-lane roundabouts and the driving speeds through them. Accordingly, speed analyses were conducted for numerous theoretical roundabouts with outer radii between 15 and 25 m, designed based on swept path analysis results, were conducted. The research results showed that it is possible to offset approaches laterally on roundabouts with outer radii between 15 and 25 m, depending on the design vehicle, and that the allowable offset values increase proportionally with the roundabout outer radius. The analysis results were used to create a design model for urban single-lane roundabouts with lateral approach leg offsets enabling their adaptation to spatial constraints while maintaining safe operating speeds.

Available sight distance (ASD) on motorways represents the unobstructed line of sight from the driver’s perspective to an obstacle on the carriageway, which must equal or exceed the required stopping sight distance (SSD). This study evaluates ASD across both two-dimensional (2D) and three-dimensional (3D) motorway alignments, encompassing right- and left-hand horizontal curves combined with different vertical alignments, as well as roadside and median barriers. 2D analyses were performed on predefined theoretical profiles, while 3D ASD evaluations were conducted on real-world models of existing motorway sections in Croatia. These sections were selected based on their diverse horizontal and vertical geometric alignments, design eras, traffic characteristics, and historical crash data regarding collisions with obstacles. The findings reveal that safety barrier placement on motorways can severely constrain sightlines, demonstrating that even radii exceeding the regulatory minimums are insufficient to guarantee necessary SSD requirements. Visibility restrictions from safety barriers are especially pronounced along barrier-restricted horizontal curves, primarily on right-hand curves and occasionally on left-hand curves, depending on the radius. In certain real-world sections, cut slopes also restrict the required visibility. Current Croatian guidelines rely on 2D analysis, which fails to account for safety barriers obstructing visibility. This research emphasises the critical necessity of conducting continuous 3D sight visibility simulations during initial design phases, while recommending further research that could be implemented to update regulatory frameworks regarding parameters for ASD analysis.