Mountain Roads’ Geometric Design: Methodological Proposal for Hairpin Bend Design/Retrofitting

Abstract

Mountainous roads often have to overcome considerable differences in height, which is why hairpin bends find a valid and common use. Despite this, there is a lack of specific international standards. Given the absence of a national standard governing the mountain roads’ design, in Italy, as in many other countries, the Swiss standard SNV 640198a is generally applied. This standard does not guarantee the correct geometric design of hairpin bends for Italian vehicle fleets and fleets according to the Directive 2002/7/EC. In this paper, the authors have developed a new methodology based on the Swiss standard upgrade, which is applicable internationally. Starting from hairpin bends’ geometric layouts provided by SNV 640198a and from related considerations, respectively, to the gyration formulae use and to swept path analysis’ simulations, they developed new planimetric layouts compatible with the vehicle fleet and with the cross-sectional dimensions of Italian roads. In this way, a generally valid methodology applicable to any international context was defined. In particular, the study allowed the definition of new geometric layouts to be used in hairpin bend design/retrofitting when it is necessary to guarantee the simultaneous entry into the bend of a 12 m long bus, and a car travelling in the opposite direction. Finally, the proposed methodology was applied to a mountain road case study in the Lucanian Dolomites area; an area of great tourist, cultural and environmental interest in southern Italy.

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

“…By applying these short lines, the vehicle path is simulated in the time it takes for the driver to turn the vehicle's steering wheel when changing the direction of movement, which results in a realistic representation of the vehicle's movement trajectories [9]. The second approach to the construction of the path (hereinafter referred to as A-2) implies the application of consecutive circular arcs without straight lines inserted between them, following the principles of hairpin bend geometry [9,11]. This approach is simpler and faster than the A-1, as fewer geometric elements are required for the construction of the path, and it is in line with the field test results discussed in [12], which have shown that at a low driving speed (under 20 km/h) the steering gear of long, articulated vehicles can follow a steering path lacking transitions without significant departures.…”

“…"Large deviations" were not recorded at cross-sections on circulatory roadway entries (1-3) for outer radii under 14.5 m and over 22.0 m, cross-sections on the circulatory roadway (4-10) for outer radii over 16.5 m, and cross-sections on circulatory roadway exit (11)(12)(13) for outer radii over 19.0 m.…”

“…Deviations are proportional to the outer radii for cross-sections on the circulatory roadway (4-10) and circulatory roadway exit (11)(12)(13)).…”