this report describes a method of estimating the distribution of speeds of cars at an average point on a length of motorway or other dual carriageway, developed from wardrop's moving-observer method of estimating journey times. it is assumed that the speeds are normally distributed, but it is shown that considerable departure from normality can be tolerated. the method consists of making several test-car runs at each of two different constant speeds, and counting the numbers of overtaking cars ("overs") and cars overtaken ("unders"). the unders-to-overs ratio at each speed is plotted on an analysis diagram, which then shows the mean speed, the standard deviation of speed, and the main percentage points of the speed distribution. (a).

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