Greenwood Engineering’s TSD Truck
While the use of traffic speed deflectometer devices (TSDDs) has been around a number of years, complete with MnROAD testing the TSD truck, departments of transportation like South Carolina are considering the technology for use in pavement management systems (PMS) as of late. The technical report “Evaluation of Traffic Speed Deflectometer for Collecting Network-Level Pavement Structural Data in Tennessee,” authored by Baoshan Huang, Miaomiao Zhang, Hongren Gong and Pawel Polaczyk, released May 2022, found that TSD testing is time-efficient and suitable to identify weak sections and weak layers of pavements. The device used in the Tennessee research was the TSD from Greenwood Engineering. Here’s how it works:
The truck drives over the network to be evaluated at posted traffic speeds.
In the TSD, a set of 10 or more Doppler lasers sends out a well described signal, which when reflected from the moving pavement has changed wavelength depending on the pavement velocity.
The Doppler lasers measure the pavement-motion in front of and behind the load wheel to picture the full deflection bowl, and in the longitudinal centerline between the twin tires of the trailer.
The TSD provides the full picture of the deflection bowl with well-known values like Surface Curvature Index 300 (SCI 300), maximum deflection (d0) and more. Servo system and inertial units continuously monitor and control the position of the Doppler sensors.
Subsystems—like the surface imaging system, right-of-way-imaging or ground penetrating radar—mounted on the dash of the truck’s cab and/or on the back of the trailer, gather additional data from the road.
Data from subsystems are synchronized with the structural data in real time, resulting in a set of all data for the road network, all obtained in one drive. The data can be displayed in web-based map systems, if the user desires.
Read the 71-page report, RES2020-08, at http://www.tn.gov/.