The signs are known as Speed Indication Displays (SIDs) and form part of an ongoing speed awareness campaign.
In essence, a portable SID sign is able to detect the speed of oncoming vehicles with a set range and display an LED display back to the driver indicating the speed of that vehicle along with a happy or sad face depending on compliance with the prevailing speed limit.
In addition, the device can capture speed and vehicle flow data for future analysis.
The Road Safety Team at Sheffield City Council has developed a system of programmes and schedules for Speed Awareness Campaigns with some of the Community Assembly Areas whereby they provide the team with a list of sites where speeding has been a cause for concern either to residents or brought to the attention of officers by local Members.
The SID sign(s) are then rotated around these sites on an eight-weekly basis and data gathered to be assessed against ‘before’ data where available in order to assess their effectiveness.
The reason for this approach is that recent studies on the use of SIDs and Vehicle Activated Signs (VASs) have concluded that they are most effective when rotated around a number of sites as this reduces the likelihood of driver familiarity with a specific sign in a specific location.