more and more speed cameras are being installed om Britain's roads in order to bring down the number of serious accidents and make motorists aware of the dangers of driving too fast. The police, who are backing this move, are in favor of making the cameras highly visible - many of them are placed in bright yellow boxes, so that drivers can see them from a distance and slow down. appears to run counter to these initiatives. Officials at the Land Transport Safety Authority in Wellington discovered that hidden cameras were actually more effective than visible ones in reducing driving speeds on all roads. Although drivers were not able to see the cameras, warning signs indicated the start of the speed camera zone, and it seems likely that motorists drove more cautiously overall because they did not know the exact location of the cameras . Overt cameras, on the other hand, had only a localised effect, by reducing actual accidents on the few metres of road covered by the camera.