Traffic Speed Deflectometer
Bearing Capacity
The bearing capacity of roads or rails can be judged by the deflection pattern from a heavy load.
To measure deflections on roads and rails while driving at normal traffic speeds has proven to be a difficult task.
Greenwood Engineering has patented a measuring concept using Doppler laser sensors in an effort to solve the problem.
Traffic Speed Deflectometer Concept
The basic idea of the Traffic Speed Deflectometer concept is to measure the velocity of deflection rather than displacement, see measuring principle.
As the velocity of deflection is the derivative of displacement it is possible to calculate the displacement subsequently, see results.
The fifth TSD is under construction
In 2012 the fifth TSD is being constructed for SANRAL, South Africa, read more.
This TSD uses 10 Doppler lasers and also includes the LaserProf and Right-of-Way imaging.
In 2011 the fourth TSD was delivered to IBDiM in Poland, read more.
In 2010 a TSD with 7 Doppler lasers was delivered to ANAS in Italy, read more
The first two TSD devices are constructed with 4 Doppler sensors and have been measuring for more than 5 years.
These are owned by respectively the Danish Road Directorate and by TRL/Highways Agencies in the UK.
TSD network measurements in Denmark
The TSD is capable of making continuous bearing capacity network measurements.
For example the Danish TSD, operated by the Danish Road Directorate has measured the Danish state road network - approx. 3300 km - since 2005,
an example can be seen at the results page.
In this example road repair work can be seen in the bearing capacity measurements.
Cost-benefit analysis
Because the TSD measures at traffic speed it is possible to measure several hundred kilometers of road per day.
This is a high production capacity compared with other stationary or slow moving bearing capacity equipments.
Furthermore, the TSD data are continuous and there is no need for road closure when measuring.
