Concept patented by Greenwood Engineering
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.
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.
Trafic Speed Deflectometer - TSD - operating worldwide
Through the early 2000 the world’s first Doppler-based TSD, configured with 4 Doppler sensors, was developed and patended by Greenwood Engineering. Two of this first-generation TSD’s was manufactured.
The first is owned by the Danish Road Directorate. In 2009/10 this equipment did measurements in cooperation with ARRB Group in Australia, read more.
The second is owned by Highways Agencies in UK. In network measurements this TSD is operated by commercial staff trained by TRL, read more.
In 2010 a TSD with 7 Doppler Lasers and several subsystems collections synchronized functional data was delivered to ANAS in Italy, read more.
In 2011 the fourth TSD was delivered to IBDiM in Poland, read more.
In 2012/13 TSD5 was delivered to SANRAL, South Africa, read more. TSD5 has 10 Doppler Lasers and simultaneously data collection from structural and functional systems and includes LaserProf and Right-of-Way imaging.
In 2013 the sixth TSD was delivered to RIOH China, read more.
In 2013 the seventh TSD was made and shipped to the US. This TSD collects both structural and functional data simultaneously and synchronized. TSD7 participated in trials at MinRoad September 2013 and a pooled fund project 2013-2015, both activities arranged by FHWA, read more.
In 2014 the eight TSD reached Australia. This TSD, acquired by ARRB, has on commercial conditions covered comprehensive measurement campaigns in both New Zeeland and half of the states in Australia. TSD8 is collecting both structural and functional data simultaneously and synchronized, read more
In 2015 ARRB from Australia opened an office in Pennsylvania USA and are now providing pavement surveys with TSD9 for several states in the US. This TSD combines structural and functional data collection in one run, read more.
In 2016 South Africa got one more TSD: TSD10 was delivered to the company VNA, read more.
In 2016 also China got a second TSD: TSD11 was delivered to Shanghai Municipality, read more.
In 2017 Greenwood Engineering is producing TSD12 and TSD14. The TSD12 will join TSD8 with ARRB in Australia, and TSD14 will go to BAST in Germany.
TSD network measurements in Denmark
The TSD is capable of making continuous bearing capacity network measurements. The Danish TSD, operated by the Danish Road Directorate has measured
the Danish state road network 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 per day.
This is a high production capacity compared with other stationary or slow moving bearing capacity equipment's.
Furthermore, the TSD data are continuous and there is no need for road closure when measuring – a very safe device.
Deflection Velocity – Dynamics
As TSD measures the vertical pavement velocity at each Doppler laser position, it is the dynamic response to the authentic design axle load that is measured. Instead of trying to simulate the load pulse from a truck, it is the axle load of rolling wheel that creates the deflection velocities. With the authentic dynamics recorded, pavement engineering research can develop new design procedures based on the dynamic features. Rolling Deflectometers using triangulation lasers cannot provide pavement dynamic response. As most pavement works are focused on pavement preservation, the benefit from TSD data will be huge due to the exact location of sections where damage develops faster than at neighboring sections. Pavement preservation actions become more reliable, and their performance can be followed year by year. This can be included in contract warranty conditions. Road authorities and concessionaires can rapidly monitor impact of heavy traffic for instance mining trucks.
