CAMERAS that detect vehicles blocking yellow box junctions are increasing congestion rather than improving traffic flow, a study has found.

Motoring groups believe that longer queues are caused by drivers hesitating before entering the boxes because they fear they will be fined £100.

More than 100,000 drivers have received penalties in the past two years for stopping in yellow boxes. They were caught by closed-circuit television cameras, which were introduced in London in 2004 and are to be installed nationwide to record minor traffic offences.

The cameras were supposed to reduce queues and journey times but Transport for London (TfL) has now admitted that traffic flow has fallen at junctions since the cameras were installed.

Many drivers wait an extra few seconds after the box has become empty or fail to follow other vehicles into the box when the exit is clear for the driver in front.

TfL studied traffic flow at the junctions before and after the cameras were installed and found that up to 150 fewer vehicles an hour passed through yellow box junctions once camera enforcement began.

Some of the 16 boxes in the study showed an improvement in traffic flow but overall it was 4 per cent worse. The cameras did, however, reduce by 23 per cent the number of drivers stopping inside the boxes .

Jeroen Weimar, TfL’s director of transport enforcement, said: “We are concerned by the results because the justification for the cameras was that they would improve traffic flow.”

Further monitoring would be carried out this summer to confirm the findings. If it was clear that the cameras were not working, TfL would consider redesigning the junctions or even removing yellow boxes.

Kevin Delaney, the RAC Foundation’s road safety manager, said: “Before the cameras went up, people were more willing to drive into boxes in marginal situations where they might have to stop on the edge.

“Now many won’t even enter the box until they are absolutely certain they will be able to get out without stopping.”

He said many boxes were badly designed, which made it difficult for drivers to avoid being caught in them.

The Highway Code says drivers should enter a box only if their exit is clear or if they want to turn right and their exit is blocked only by oncoming traffic or other vehicles waiting to turn right.

CCTV cameras are also used to detect drivers who stop in no-waiting zones, make illegal turns or drive the wrong way down one-way streets.

The cameras are installed on main roads across London controlled by TfL and other roads in the boroughs of Camden, Croydon, Ealing, Hammersmith & Fulham, Haringey, Islington, Lambeth, Newham, Wandsworth and Westminster.

The Department for Transport plans to give similar powers this year to local authorities outside London.

The cameras, which are often erected on buildings or poles above a driver’s field of vision, have been criticised for being difficult to see.

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