The traffic signs that smile at you when you go the right speed have no effect on the average driver.

That’s the conclusion of a study of Speed Indicator Devices (SIDs) by the Transport Research Laboratory.

But in one part of Kent they have been given the thumbs-up.

Three of the ten test sites were in Metropolitan Kent - Bromley and Bexley.

The radar devices indicate with a smiley face or a frown whether the driver is going too fast.

The conclusion of the TRL study appears to show these have merely a novelty effect on drivers.

The speed of cars before the SIDs were installed was measured along with the average speed while they were in place and after they had been removed.

Over all the average speed of vehicles went down by just 1.4 mph, while the SID was in place and that figure was mirrored at the Kent sites.

Despite the interactive sign being in place though, almost half of all drivers were still exceeding the speed limit at the ten test sites, and it seems in Bromley and Bexley the signs have even less of an effect.

Before the SID was put in place at Welling Way, Bexley, 86 per cent of drivers went over the 30 mph limit and this fell to 65 per cent when the device was in place.

At Kings Hall Road, Bromley, the device also had little affect on drivers’ speed with 66 per cent still going too fast after the device was in place compared to 72 per cent beforehand.

However, it did seem to make more of a difference at Bromley Hill, Bromley, with 63 per cent before and 39 percent during the SID’s placement going over the speed limit.

At all sites the average number of people exceeding the limit went back to previous levels once the SID had been removed.

Despite the study's findings, Bromley Council believes the signs are a "useful" tool for killing speed.

Bromley council spokesperson Andrew Rogers said: "The SIDs are an effective road safety measure and helps remind drivers the speed they’re driving at if they’re exceeding the limit and we would view them as a useful part of a range of safety measures."

The smiley faces are not something KCC is using at the moment but should they be used? Do you think seeing a frowning face will make you slow down? Leave a comment below.