London, Oct 5 : Roadside speed indicators that display a face frowning when motorists exceed the speed limit are being widely ignored, a new study has revealed.
Hailed by motoring groups as the driver-friendly alternative to cameras, they have become increasingly popular with councils and police, given that they cost around 3,000 pounds each compared to 20,000 pounds for a camera, and are used on more than 1,000 roads.
But the radar devices, which display each vehicle's speed as it passes with either a smiling or frowning face, are said to have only a "novelty effect" on drivers.
Motorists slow down for the first week then quickly resume their bad habits.
After three weeks, speeding is just as bad as before - and in half the sites tested even more drivers broke the speed limit when the devices were removed than did so in the period before they were installed.
The study, which was commissioned by Transport for London (TRL), involved 10 sites on roads with 30mph limits in South London, Surrey and Kent.
Drivers' speeds were measured before, during and after the devices were installed.
It found that the average speed of vehicles passing the sites fell by 1.9mph in the first week, but that the impact then began to wear off.
During the second week, the reduction in average speed was only 1.6mph, and this continued to deteriorate in the third week.
Even in the first week that devices were installed, their effects were short-lived, with drivers accelerating back over the limit within a few moments of passing.
"This report underlines that these devices have only a limited effect and are not enough to protect communities from dangerous drivers," Telegraph quoted Robert Gifford, the director of the Parliamentary Advisory Council for Transport Safety, as saying.
"They have a short-term effect but it would be a mistake to think that they alone can solve a speeding problem. Other measures, such as road humps and camera enforcement, are needed to bring down speed in the longer term," he added.