Track Width for a Safe Travelling of a Timber Tractor-Trailer Combination

In Italian Alpine Regions, wood transportation from the forest to local terminals is commonly practiced using low powered tractors with trailers (equipped with single axis or two axes) on steep downhill tracks, that must be wide enough when cornering. Aim of the work was to study and to define a calculation model to detect the width of the turning carriageway as a function of the turning radius of the vehicle used in the forestry sector for timber transportation. When a tractor-trailer system turns, four trajectories are plotted, drawn by the wheels of the tractor and by the wheels of the trailer. The overall width of the carriageway to make the turn possible is given by parameters depending on some vehicle characteristics, and it can be summarized as the difference between the radius of the circumference described by the external front wheel of the tractor and the radius of the circumference traced by the innermost wheel of the trailer. The track width is therefore function of two parameters: the distance between the hitch and the rear axle of the tractor, and the distance between the towing eye and the trailer axles. The calculation model studied in this work identifies the internal radius of the curve and the width of the carriageway necessary for the transit of a tractortrailer system. A correct design of the forest track accordingly to the dimensional needs of the vehicles is essential for a safe driving, especially in the case of the downhill timber transportation.