Speed Indicator Devices (SIDs) are temporary vehicle activated signs which detect and display real-time vehicle speeds. This report presents the results of a study of their effectiveness in reducing vehicle speeds in London that was carried out in 2007 by TRL on behalf of Transport for London.
The specific aims of this study were to assess the effectiveness of SIDs over time and distance at several locations in London. SIDs were installed at eleven sites in South East London for one, two or three weeks. Vehicle speeds were recorded at each site from one week before the SID was installed until two weeks after it was removed. SIDs were found to be effective at reducing vehicle speeds on 30mph roads in London when deployed for a short time.

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