Slope Rounding Influences on the Trajectories of Vehicles

Slope rounding is discussed in the Roadside Design Guide as a practice that breaks the sharp edge in a highway cross section and the side slope. There have been past studies aimed at understanding the influence of slope rounding on vehicle trajectories for various slope conditions. These studies were conducted about twenty years ago and only looked at a small subset of vehicle types despite the recognition that the size and weight of vehicles influences the slope rounding effects. This research effort analyzed two current vehicle types using vehicle dynamics analysis tools. These tools simulate the response of the vehicle to varying surface features for given road departure speeds and angles. The analysis considered various shoulder conditions and rounding treatments for the transition to 4:1 side slopes. The trajectory plots for the 1100C and 2270P vehicles departing the road at speeds of 30, 40, 50, and 60 mph and angles of 15 and 25 degrees were generated using simulation. The results show similarities to the previous research, expand the knowledge about the effects of slope rounding for other conditions, and suggest a means to systematically develop guidance for determining how and where to apply slope rounding. Working Paper NCAC 2011-W-004 January 2011