Arrival Turning Flows
Average Daily Traffic
Calibration of Road Capacity
Geometric calibration applies both to the slope and intercept of the capacity line.
Entries and bypasses can be separately calibrated.
The intercept in modified by an + an absolute value to achieve the measured value. The size of the intercept change is explicit.
The slope is modified to the measured by using a slope factor. The change in the slope is explicit. For calibration measurements roundabout entries must be at genuine saturation capacity for at least 30 continuous minutes.
Capacity measurements must be made for large sample of roundabout entries to give the capacity lines and their distribution.
The mean of such a distribution is the calibrated value.
Using data from one or two roundabouts is hopelessly inadequate as this gives an unknown random point on the capacity distribution, not the mean that is needed for comparison with the mean capacity prediction of the model. Only "means" can be sensibly compared to "means". Comparing an observed random point on the capacity distribution with the predicted mean is more likely to uncalibrate than calibrate the model.
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