GBG Australia
Suite 4/8-10 Palmer St
North Parramatta
NSW 2151
phone: +61 2 9890 2122
fax: +61 2 9890 2922

Pavement Surveys

Traffic Speed Radar

Faced with shrinking budgets and longer term 'ownership' of responsibility for maintenance, today's pavement engineer requires more information on the construction and condition of pavement structures than ever before. At the same time a premium has been placed on highway access and the engineer must consider the impact of lane closures and traffic management schemes causing delays incurring possible political and financial penalties.

These pressures have encouraged the development of high speed data collection systems to determine pavement construction and condition on a network scale. Impulse or ground penetrating Radar is one of these systems and can be used in checking compliance of new construction, gathering information on a network for management purposes or for aiding in the design of large scale road treatments.

Principles

Radar works by transmitting bursts of radio frequency pulses into the pavement. As each wave or signal passes through different layers its velocity changes and part of the signal is reflected back to the surface. The strength of the reflection mainly depends on the difference in propagation characteristics (dielectric constant) of the adjacent layers. The greater the difference the stronger the reflection.

The radar fires pulses at fixed time intervals as it passes over the road surface and records the shape, amplitude, frequency and travel time of the reflected signals. To convert this data into cross sectional image of the pavement, a calculation is made to convert the travel time of the reflected signal into depth, and interpretation is required to relate the changes in the data to actual material layers. This requires the use of powerful processing software by experienced personnel

Logistics

Investigations are typically conducted from an appropriately marked vehicle using digital radar systems with the ability for multiple antenna configurations. The antenna are mounted in front or under the vehicle and maybe air coupled for ease of use at high speed or ground coupled for better resolution at depth.

The resolution of pavement features depends on the sampling rate of the system, which is controlled by the scan rate of the radar and the travel speed of the vehicle. At 70 - 80 kph the typical sample rate is 1 recorded scan every 0.2m . Therefore features smaller than 0.6m lateral extent may be missed. More detailed subsurface information such as base and sub-base layer thicknesses, asphalt layer condition information and locating voids under slabs or buried utilities requires much slower recording speeds in the order of 3 - 7kph.

The radar data may be referenced to standard section lengths provided by the client as it is collected. The use of automated distance measuring and sampling rate adjustment systems enables a high level of relocation accuracy.

Reporting

GBG Australia are committed to the principle of presenting the results of an investigation in the format most suited to the clients needs. Generally high speed network data is presented in a tabular, database format for inclusion in an asset register. Data can also be presented in a graphical format and longitudinal sections can provide a better combination for detail and perspective. All formats can generally be provided in hard copy and/or digitally. All results are accompanied with a written report.

Summary

Traffic speed radar investigations can enable the highway engineer to make better informed decisions by providing a better overview of the construction of the networks pavements and highlighting parts of a network requiring further investigation. The method has the following principle benefits and limitations:

Benefits Limitations

GBG Australia have undertaken investigations of: