Streets ahead

A new road survey vehicle was launched last week that will allow data to be collected from Britain’s roads 30 times faster than conventional methods.


A new road survey vehicle was launched last week that will allow data to be collected from Britain‘s roads 30 times faster than conventional methods, ensuring less disruption to motorways and major roads around the country.

The Traffic Speed Deflectometer (TSD) can survey the structural condition of roads at speeds of up to 50mph, leading to fewer delays for drivers. The acquired information, when combined with data gathered by other types of survey, will give the Highways Agency a more comprehensive picture of the condition of the strategic road network, making it easier to target maintenance and allocate resources where needed most.

Brian Ferne, senior research fellow at the Transport Research Laboratory (TRL), who is carrying out the project for the Highways Agency, said the basic principle in testing a structural component is to measure the deflection, (defined as pavement move under load) the measure of which will indicate the strength. Therefore it will indicate how long a road should last or how much strengthening is required.

The TSDA, acquired from the Danish Road Institute, uses non-contact laser sensors to measure the vertical velocity of the road as it moves away under load. Four sensors are fitted to the lorry; three near the load-bearing axle and one well in front of the loaded wheels that enables further corrections for unwanted movement and rotation of the sensor mounting frame. The aim is to discover the relationship between the deflection response, as measured by TSD, and the structural condition of the road.

The new technology costs more initially but, as TSD’s productivity is much higher and does not require expensive road closures, it will be more cost-efficient in the long term.

Assessing the structure of the road to ensure the lower levels support the upper levels is an ongoing job. The entire 4,500 miles of motorways and major A roads are surveyed at least once a year.

Conventional techniques employ a Deflectograph, a device that originated in France comprising an 11-tonne, twin-axle rigid lorry that uses a mechanical system to measure the vertical response of the road to the load.

The UK has 12 operating around the country, but Ferne said: ‘These only work at walking speed up to 2.5 km/h but the coverage they have been doing has been steadily curtailed because of disruption they cause. We have been looking at what other techniques could do this at traffic speed.’ He believes the Highways Agency will be able to commission network surveys by 2009.