SID Traffic Data
Shorne Parish Council operates a speed indicator device (SID), which is periodically moved between fixed locations at Pear Tree Lane, Tanyard Hill, and Thong.
It is set to display information to oncoming traffic to help educate and inform drivers. It displays the speed of vehicles travelling between 27 mph and 30 mph. For vehicles travelling over 30 mph and up to 40 mph, it displays a “Slow Down” message in addition to the vehicle speed. For vehicles travelling above 40 mph, it displays the “Slow Down” message only.
The SID records data regarding traffic volumes and vehicle speeds by the hour, day, week, etc, and we are able to analyse the data in detail. This is where we will periodically post brief summaries of the traffic data recorded.
Perhaps the most useful data for comparison purposes is the AADT (Annual Average Daily Traffic) which provides the average number of vehicles which pass the SID location in one direction per day. The total number is less important, since it will vary depending on the length of time that the SID has been in situ at any particular location.
The 85th Percentile Speed is also important, as it is the speed at or below which 85% of vehicles travel. It is often used in setting speed limits and in determining whether the existing speed limit is appropriate. If, under free-flow conditions, 85% of traffic consistently travels at a significantly higher speed than the existing speed limit, then the limit may be raised. If, under free-flow conditions, 85% of traffic consistently travels at a significantly lower speed than the existing limit, then the limit may be lowered.
The “enforcement threshold” is the speed at or above which the Police may take enforcement action on an offender. This is calculated from the applicable speed limit plus 10% plus 2 mph, which for a 30 mph limit equates to 35 mph. Shorne’s Speedwatch volunteers regularly carry out sessions at the SID locations, and report any vehicles observed travelling at or above the enforcement threshold to the Police.
There will unfortunately always be the odd vehicle recorded travelling at high speed, irrespective of the speed limit. The SID does not identify whether these are emergency vehicles or reckless drivers. Thankfully detailed analysis of the SID data shows that these are relatively isolated occurrences, and that the vast majority of vehicles travel within or close to the speed limits.
The attachments below are shown with the latest data at the top, oldest at the bottom. Inevitably, traffic volumes since March 2020 have been affected by the varying stages of lockdowns and school closures due to COVID-19, and road closures can also have an impact on traffic volumes.