9.3.1 Ramp Gradients for System Interchanges
The ramps on system interchanges are either direct ramps or semi-direct ramps and provide for relatively high-speed movements (≥ 80 km/h) between major arterial roads (e.g. freeways). Therefore the vertical geometry should be chosen to enable ramp traffic to move between the major roads efficiently and safely. For this reason the gradients used should accord with those used for rural arterial roads (refer to AGRD Part 3 (Austroads 2010b)). It is recommended that the preferred maximum gradient is 3% with an absolute maximum of 5%.
The choice of gradient on these ramps should take account of the high number of trucks that use such facilities and ensure that an appropriate level of service is provided (refer to the Guide to Traffic Management Part 3: Traffic Studies and Analysis (Austroads 2013d)). However, system interchanges often occur in urban areas where sites are constrained and minimum gradients may not be feasible, and as these ramps are relatively long, two-lane ramps are usually provided to enable slower vehicles to be overtaken on rising gradients.