Car Speeding Test Results

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Results from Speed Tube readings

One set of speed tubes was laid outside Cedar House/Robert Shaw Trust field, the other alongside the pond. Readings were taken from both, in both directions, over seven days – 14th to 21st March. [It should be noted that it is perfectly possible for traffic to generate no reading e.g. a Winchmore Hill resident travelling to the school would not generate a reading.]

Over the seven days there were 915 readings at Cedar House but only 616 at the pond. This significant difference could possibly be explained by school visitors, the majority of whom will make four runs per day or twenty per week. Figures given by Jenny Earp confirm that the school demographic may well be skewed to the north of the village (with Winchmore Hill children not triggering readings) and that this would therefore seem to explain much of the imbalance.

A further feature of the data concerns peak morning and afternoon/evening traffic. At Cedar House the peak a.m. volume is 95 at 08:00¹ while that for the pond is 44 at the same time. At Cedar House the peak p.m. volume is 86 at 17:00 while that for the pond is 73 at the same time. I would suggest that the differences might be attributable to commuters heading to and from Amersham station.

Observations:

Speeding in general would appear not to be a problem, possibly suggesting that our perception of speed, as pedestrians, is over-estimated. The mean average of readings at Cedar House was 28 mph and at the pond 26 mph.
However, at the 85th percentile (“the speeds at or below which 85% of all vehicles are observed to travel under free-flowing conditions past a nominated point”), the 24 hour reading at Cedar House was 34 and that at the pond was 33. These figures, the average over seven days, suggest that there may be a speeding problem and legally that has to be the case.
At Cedar House the 85th percentile reading was highest at 37, taken during the hour beginning 06:00 (there were additionally readings of 36 at 07:00 and at 17:00).
Similarly, at the pond the 85th percentile reading was highest at 35 during the hour beginning 07:00 and 17:00, suggesting faster rush hour traffic.
The tubes do not appear to have led to lower speeds after day one.
At Cedar House:

There were 917 readings (131 per day): 423 one way; 494 the other
72.1% of the readings were of speeds below 31 mph and 92.3% below 36 mph
7.5% or 7.7% (rounding error) of the readings were at speeds above 36mph
There was no reading above the 41-46 mph bracket
There were three readings in the 46-51 bracket and one in the 51-56 bracket

At the Pond:

There were 616 readings: 345 one way; 271 the other
79.9% of the readings were of speeds below 31 mph and 94.6% below 36 mph
5.4% of the readings were at speeds above 36mph
There was one reading in the 46-51mph bracket which was taken at 17:00. But the total for that speed bracket shows zero so there has to be uncertainty as to the veracity of this reading.
There were two readings in the 46-51 bracket and one in the 51-56 bracket

The lack of consistency in the readings between the weekly totals of each speed bracket and the hourly totals of higher speeds has been noted above. It is also worth mentioning that there were only ten readings above the 4146 mph bracket or 0.7% of the total sample.