Grade measurement with an instrumented car

Grade information may be needed for route surveys and is important when fuel consumption is studied. An instrumented car was used to measure acceleration along the road surface by double differentiating accumulated pulses generated off the drive train. A second acceleration measure included the component due to gravity relative to the car body. The difference between these acceleration measures contains grade information but it also influenced by suspension dynamics and pitch of the car body. The effect of suspension dynamics was removed by filtering which limited the minimum wavelength to 160 m. The effect of pitch was removed by a correction based on acceleration, jerk and the square of vehicle speed. The correction was computed from data collected on a level airfield runaway. The method is verified for a high capacity arterial road. Grade is measured to within 0.001 rad (95% confidence limits). Elevation derived from the grade data was consistent with road construction drawings to the same limits.