The Design Vehicle Steering Path Construction Based on the Hairpin Bend Geometry—Application in Roundabout Design

Abstract

A prerequisite for a well-designed roundabout is the definition of the design vehicle movement geometry and its turning envelopes. This is because kinematic and dynamic requirements lose their importance due to low driving speed. In this paper, the investigation of the deviations of design vehicle steering paths for straight passage through the roundabout constructed according to the two approaches is presented. The first approach (A-1) includes the application of short, straight lines between the adjacent arcs on the path, and the second (A-2) implies the application of consecutive circular arcs. A computer simulation of vehicle movement was conducted using the Autodesk Vehicle Tracking 2020 software. The results showed that A-2, a faster and simpler approach, is applicable with caution, as the resulting turning envelopes derived from this approach are more offset from the roundabout centers compared to the A-1 approach. A total of 72% of right-hand-side path and resulting right-hand-side design vehicle body and chassis turning envelope deviations were between 0.00 and 0.15 m, 27% were over 0.15 m, and 7% were over 0.25 m. This results in larger roundabout entry and exit widths as well as the need for large lateral clearances for entries and exits on roundabouts where heavy pedestrian traffic on sidewalks is expected. The noted offset of left-hand-side design vehicle trajectories on the circulatory roadway (which was mostly between 0.05 and 0.15 m) could have a positive impact on the deflection around the central island.

Speed Reduction Capabilities of Two-Geometry Roundabouts

“…Paths for the right turn (shown in pink in Figure 1b) were constructed with an entry line that was offset by 1.75 m from the splitter island on the roundabout entry, an exit line that was offset by 2.0 m from the splitter island on the roundabout exit, and a circular arc (R ) tangential to these lines. Paths for straight passage (shown in orange and green in Figure 1b) were constructed following the principles of hairpin bend geometry, i.e., with an entry line, three consecutive circular arcs, and an exit line, as elaborated in [25]. Entry and exit lines were offset by 1.75 m from the splitter island on the roundabout entry and exit.…”