A new round of roadside traffic surveys will take place at three sites in Carlisle tomorrow.

The county council, however, is not saying where they will be so that drivers do not change their journeys.

Similar unannounced surveys last month caused a major outcry that prompted an apology from the authority.

They caused major congestion problems and the county said they would be suspended at key times to ease problems.

Tailbacks were so severe that Trinity School was forced to delay the start of an exam, motorists were late for work and commuters reportedly missed trains.

Cumbria council says it recognises the frustration and inconvenience caused by one particular census on Eden Bridge - and says it has learned its lesson.

"The delays on Eden Bridge were made worse by the inclement weather and two vehicles which broke down within a short space of time, requiring the vehicles to be ushered in to the closed survey lane on the bridge.

"Surveys at Warwick Road and London Road during the same programme did not experience the same problems and traffic was able to flow much more freely.

"Extra efforts will be made to ensure the free flow of traffic at each site on July 13 and officers will halt surveys if congestion becomes a problem," said a spokesman.

The surveys involve stopping a sample of drivers and asking them to answer questions about their journeys.

Each survey site is operated in one direction only, with interviews expected to take between two and three minutes.

Traffic controls will be provided by Cumbria police.

The surveys show how, why and where people travel across Carlisle to help make the case for investment in the road network.

"We do not publicise specific site locations as we need to capture typical travel patterns; understandably people may change their route which could distort the results," added the spokesman.

"Other data sources for travel patterns are available and were explored - such as Automatic Number Plate Recognition cameras - but these do not capture key information such as trip purpose. Roadside interview surveys are the most reliable way of collecting this information."