Standard Deviations
We now have standard deviations (σ) in Path Analysis for Road Intelligence. You can view standard deviation in either mph or km/h. Toggle between imperial and metric measurement systems under the Measurement Settings tab, located under the profile icon at the top right-hand side of the screen. We've added:
- A Standard Deviation Speed Analysis Graph
- As a column in the Speed Analysis Summary Table
- As a column in the Speed Bins Summary Table
- A Standard Deviation G-force Graph
In the speed bin table and summary table you will now see a column for the standard deviation. There is also a chart variant for this data. This data is not backdated, meaning old files will not include the standard deviations. Users can re-query the data if they want to obtain it, but it will be present for all future requests after deployment. It is also present in all metric responses from the API.
We've used the following equation:
It allows users to understand how consistent speeds are on different roadways. Each standard deviation away from the mean indicates where a certain percentage of the data lies. Meaning, within one standard deviation either side of the mean (average speed), 68.2% of the data is there.
An Example
If a path analysis query had a mean of 75km/h (46mph), and a standard deviation of 5km/h (3mph), ~70% of the data would be within 5km/h (3mph) of 75km/h (46mph). This indicates a significant portion of the data lies within this range.
If the standard deviation were 15km/h (9mph), the data is distributed more widely. This implies a higher 85th percentile and lower 15th percentile. You could use this to understand if the range of data has improved over time due to traffic calming measures. It also allows better understanding what constitutes an outliner and what does not, since the know what standard deviation the value lies within.