Establishing the Minimum Ground Clearances for the TAC Design Vehicles Based on the Desirable Grades and the Maximum Grade Changes

The TAC Geometric Design Guide for Canadian Roads (GDGCD) 1999 describes the turning
characteristics of design vehicles using turning templates. Vehicle turning templates play an
integral role in controlling the horizontal aspects of the geometric design of intersections. As to
the vertical aspect of a design, design vehicles are ignored primarily because no information is
provided on the vehicle’s ground clearances nor the pitch and roll limitations at the vehicle’s
articulating points. Hence, vertical profiles are not typically evaluated against the standard
design vehicles in practice, but instead it is assumed that the maximum recommended grades
and grade changes for the vertical alignments presented in the design guideline will
accommodate the vehicles. With ground clearance values implied, designers cannot easily
perform checks to ensure the vertical profiles that deviate from the guidelines will accommodate
the design vehicles. This may lead to potential vehicle hang-up conflicts at driveways, rail
crossings, and roundabout truck aprons. This study is focused on establishing the ground
clearances for the GDGCD design vehicles so that they can be incorporated into future guidelines.
The ground clearance for 8 of the design vehicles is calculated as a function of the recommended
grades in the GDGCD and verified against 3D vehicle simulation software. A more comprehensive
study involving surveying the existing vehicle inventory in Canada to establish these ground
clearance values is recommended but is not covered in the scope of this study.