Combining the carrot and stick: can ANPR Speed Indicator Devices reduce speed in rural areas?

Suffolk County Council

Amount awarded


Uploaded to Knowledge Centre
30 May 2023

This report presents the findings of a research study carried out to review the effectiveness of automatic number plate recognition (ANPR) speed indicator devices (SIDs) in reducing speeds in rural areas, specifically in Suffolk.

The main conclusion of the study is there was no detectable impact of ANPR SIDs in reducing neither speed nor the proportion of speeding vehicles at selected sites.

Agilysis evaluated traffic speed data at sites where ANPR SIDs and temporary vehicle activated signs (TVAS) were located. Paired t-tests were carried out to compare sites against themselves in different time periods, to observe changes and whether these could have occurred by chance or due to the intervention.

The study found that there were no significant changes in average or 85th percentile speed (the speed at which 85% of traffic is travelling at or below), or the percentages over the enforcement threshold of 35mph, during the trial period for either ANPR SID or TVAS devices.

This was across five points in time and two one-week deployments of the devices, with publicity of the ANPR SID devices in the middle of the trial. Other studies of SIDs have detected reductions in speed, albeit for a limited period of time during single deployments.

However, for the sites in this trial, selection was based on nomination by villages and then random selection for inclusion in the study. This means that baseline speeds and evidence of an existing speeding problem were not predefined criteria. With pre-existing high levels of compliance with the speed limit, it is difficult to change behaviour to achieve an observable effect which could not have occurred by chance.

The results of this trial have revealed that site selection and integrity are critical in optimising the chances of the selected intervention producing the desired effects; and that a behavioural diagnosis or ‘mapping’ of the road safety issues at play can help to ensure that the intervention designed or selected is relevant to effectively target the problem behaviours identified.

To understand the community views of the ANPR SID and TVAS devices after the trial, a survey was issued to the parish representative involved and to local residents. The analysis demonstrates that whilst ANPR SID devices are more often associated with people driving slowly, neither device is associated with faster speeds, with both ANPR SIDs and TVAS associated with positive effects on driver behaviour. Parish representatives overwhelmingly disagreed, however, that both device types could reduce speeds more than speed cameras, with the level of disagreement that they are more effective than speed humps slightly less, despite still being the majority view for both device types.

Click the link below to read the full report: