Mobile Speed Indication Devices Policy

(A pdf version of this policy is available for download here)


Speed Indicating Devices, or SIDs, are temporary sign installations that alert road users to the speed at which they are travelling along a given stretch of the highway.

The demand for interactive signing is increasing on the highway network as the local community continues to be concerned about the perceived, and actual, number of vehicles that drive too fast through their villages.

It is the intention of St Stephen in Brannel Parish Council to supply, erect and maintain 6 mobile SIDs according to the terms set out in this policy.

Mobile speed warning signs can be used at sites where speed is a concern even though there may not be a history of crashes. However, research has shown that their effectiveness reduces over time, with little or no speed reduction after about two weeks at any one location. Similarly, overuse at a site can dramatically reduce the effect and so it is recommended that sites are used no more than three times a year.

Choosing locations

There are no legislative powers for Parish councils under the Highways Act to erect these signs on the highway therefore permission will have to be sought from Cornwall Council prior to erection at each location.

The following requirements for SID sites MUST be met:

  • The posted speed limit must be 20, 30 or 40mph.
  • The site must be inside the speed limit and the SID unit must not be placed upon the entry sign to the speed limit.
  • There must be adequate forward visibility. In a 20mph speed limit this is a minimum of 60m, and in a 30mph speed limit this is a minimum of 90m, and in a 40mph speed limit this is a minimum of 120m.
  • The SID unit must not obscure visibility of another traffic sign.
  • The SID unit must not obscure visibility from any access or junction.
  • The post/street furniture on which the SID unit is to be deployed must be safely accessible and in a good condition.
  • The SID unit must not obstruct a footway, cycle track or verge on which pedestrians walk.
  • The SID unit, including its face, must have at least 450mm clearance from the edge of the carriageway, 600mm if sited on a central island.
  • Where the SID unit is sited over a footway then a mounting height of at least 2.1m is required. If sited over a cycle track, then a mounting height of at least 2.4m is required.
  • SID units can only be fixed to existing traffic signposts or lamp columns. Cast iron or ornate lamp columns, power supply or telephone poles, and private posts must not be used.

Council will agree a 6-monthly schedule of locations in March and September to allow sufficient time for permission to be sought from Cornwall Council.

Locations will be selected

  • On recommendation from Cornwall Council
  • On recommendation from Devon & Cornwall Police
  • On recommendation from Community Speed Watch
  • By Member proposal
  • By resident feedback given to the Clerk


The SID will only be erected and dismounted on the highway by trained Parish Council staff.

The SID units will be installed in pairs wherever possible to monitor both directions of traffic.

The SID will ideally be placed at any one given location for 6 weeks but in any event, a placement should not exceed 8 weeks to retain the maximum effectiveness of managing speed

The SID should not return to the same site for a minimum of 12 weeks. This is to try and maximise the effectiveness of the SID’s deployment

The speed threshold activation limit will be set by Cornwall Council


The Clerk will manage all data and provide a report to Council on a quarterly basis. This report will also be placed on Council’s website.

Data that indicates speeding at a site will be shared with Devon & Cornwall Police and Cornwall Council.

[Adopted by Full Council at the meeting held on Wednesday 3rd March 2021 under minutes number FPC66/21. Due for review in 2024.]