While too early to draw firm conclusions, the village Speed Indicator Device (SID) has completed its first fortnight on station and so there is now data to examine. The SID was installed outside the farm shop on 27th February in the location that all previous traffic monitoring has taken place. It was felt that this was the best place to start, as we now build up a picture of traffic speeds at different points around the village. The SID cannot stay at any one location for more than 2 weeks and cannot return for a further 6 weeks. This ensures that regular traffic does not become accustomed to the sign, which in other locations has proved too be less effective over time.
GRAPHS
The average speed over the first fortnight was 31mph. It was also 31mph over both week’s individually. However, daily averages do change slightly, as shown in the first graph. At the moment there is no indication that traffic is faster on any particular day, but this graph may give the community speedwatch group a day to target in the future. The second graph is the average speed by hour. This graph is a little too crowded to decipher using a fortnight’s data but by focusing on just 24hrs, the graph shows clearly that most cars maintain the speed limit between the hours of 9am and 5pm. Outside those hours, speeds are generally faster.
Obviously, the fact that the average speed is close to 30mph means that some cars must be travelling slower and others faster. The Pie chart below shows that the vast proportion of vehicles are slowing to 30mph or below. The pie slices that represent 16-20mph, 21-25mph and 26-30mph amount to 70% of all vehicles passing the SID. 21% travelled at between 31-35mph and 9% exceeded the speed limit by a significant margin. Out of 29,579 vehicles, 3 passed the SID at over 70mph! All three were within daylight hours.
The graph below shows similar data to the Pie chart but in line format. The peak flow on every day is below 30mph and shows similar numbers of cars just under the speed limit to those just over it. Hence an average speed of 31mph.
Last but not least, the graph showing traffic density over time shows a very similar pattern every day. Traffic flow is greatest at between 8am and 9am in the morning (the high peak). Traffic volume slows during the day and builds up over an extended period between 4pm and 6pm in the afternoon (the second peak). Traffic flow drops to almost zero between 11pm and 6am (the deep trough). This pattern is repeated every day and only drops on Saturday and more on Sunday. The next week is a repeat of the same pattern.
The SID has now been moved to above the village green, facing south. Average speeds are expected to be far lower at this point but it will be valuable data to find out how fast traffic does come around the sharp corner and also to assess if any of the high readings in the last fortnight were falseor not. It will take a while to master how to set up the SID for maximum reliability and maximum accuracy.
CONCLUSIONS
It is dangerous to draw too many conclusions after just one session but it would appear that the SID has had a significant effect on reducing the speed of traffic through the village. In the past, data collected from static speed devices next to the farm shop have shown average speeds closer to 35mph. Regarding targeting of habitual speeders, the CSW would have most effectiveness between 7am and 8am on any week day. If they want to be seen by the maximum number of vehicles, then the most traffic passes between 8am and 9am or between 4pm and 5pm.
It should also be pointed out that while the A30 remains closed, it is assumed that traffic volumes are depressed and both volume and speeds may increase when there is more commuting to Yeovil, after the 25th March.
Many thanks again to those who have supported the purchase cost of the SID and if anyone is interested in assisting moving the SID once a fortnight, please respond here.
North Perrott 