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Highways and Traffic

Highways and Traffic

Speed Indicator Device (“SID”)

The Parish Council has owned SID since 2008.  SID is therefore getting a bit long in the tooth, and the Parish Council is considering the possibility of trading him in for a newer model with more advanced features (see below).  SID is deployed around the village (and occasionally further afield) at various locations.  SID’s twin purpose is to

  • Record data (number of vehicle movements, time of day of each movement and vehicle speed)
  • Display each passing vehicle’s speed with the aim of encouraging/shaming those drivers who exceed the speed limit to modify their behaviour.

SID is programmed to show a static display when a vehicle is not exceeding the speed limit, and a flashing display when it is. For vehicles substantially exceeding the speed limit the display remains  blank (so that any ‘boy racers’ can’t treat it as a challenge) but the speed is still recorded.  SID is usually deployed for only about a couple of weeks in any one location, the theory being that any deterrent effect diminishes over time.

As far as compliance is concerned, speed limits are no different to any other law of the land: there will always be some who misbehave. However, SID has shown over the years that compliance within Crondall is pretty good.   There will be many who disagree, but it is widely accepted that pedestrians are prone to significantly over-estimate the speed of passing traffic, especially (as is the case in much of Crondall) when the road is narrow.

Speed limits have historically been determined on the basis of the “85th percentile” speed: that is, the speed which 85% of drivers will not exceed under normal circumstances, even when no particular speed limit is in force, the theory being that if a speed limit is set significantly lower than most drivers consider reasonable, it will not only be widely ignored but will encourage drivers to consider speed limits in general to be unreasonable.  Current government guidelines have to some extent moved away from the “85th percentile” approach towards a “mean speed” approach, but the former is still taken into account in any evidence-based speed limit decisions, and remains a very useful guide to the reasonableness and effectiveness of existing speed limits.

Unlike SID, some more modern ‘state of the art’ equipment is capable of monitoring arriving and departing traffic with the same single deployment, and can also distinguish between cars and lorries. Data downloading is also very much simpler, as is ‘on site’ programming, making it simple to  – for example – alternate between displaying and not displaying speed (whilst all the time recording speed).

SID’s deployments during 2016/17 are summarised in the bar graphs below (please note this is not an exhaustive list of data and deployments!). With the exception of the deployment to Pankridge Street in September/October 2016 when some 17% of vehicles exceeded the 30mph speed limit, all other deployments showed more than 90% compliance.  For each of these deployments there is much more data available (for example, showing daily patterns of traffic density, and identifying when particular excess speeds occurred) that can be consulted if required.  However, the bar graphs below provide the most accessible summaries of speed, the key indicator.

We ‘re somewhat limited as to where can deploy SID as he needs to view a relatively straight section of road and also needs a strong post for mounting, but if there is a particular spot that you feel he should visit, please contact the Clerk.

Speed Indication Device (SID) Results – Feb 2017

SID Well Rd Feb 2017

SID Pankridge Street Oct 2016

SID Dippenhall Aug2016

SID Croft Lane Apr2016