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Conversion of dynamic TSD bowls to equivalent FWD static bowls: NZ Interpretation.xlsx

This process is an effective substitute for a full dynamic analysis because it enables any of the traditional widely used FWD layered elastic models to be used directly by any user.

Note that after using the above spreadsheet all TSD files must first be validated for consistency in each specific environment/terrain by using layered elastic models as checks to ensure (i) there is no persistent bias between subgrade moduli obtained in adjacent (or opposing) lanes if the TSD field testing is done on different days, and (ii) that testing in a subsequent year confirms similar subgrade moduli in each lane. This is because the outer sensors are the most sensitive in the process of bowl determination and they are controlled primarily by the subgrade stiffness.

If encountering any issues with TSD-FWD conversion, or want a site-specific conversion and validation done, you are welcome to email the basic TSD slope data spreadsheet to This email address is being protected from spambots. You need JavaScript enabled to view it.
(No service charge if it can be done with an existing model).


NZ Transport Agency, Technical Advice Note:

Use of Traffic Speed Deflectometer Results


Report on Conversion of Dynamic TSD bowls:

Traffic Speed Deflectometer - NZ Interpretation Final.pdf



MSD Summary & Application on SH6


Comparison of FWD - Multi Speed Deflectometer:

Pavement Structural Evaluation, TSD & MSD Comparison


Comparison of TSD - Multi Speed Deflectometer:

Overview and Comparison of TSD - MSD Network Asset Management


Case history: Reality check for TSD/FWD forecasting of pavement remaining life: 

RIMS Forum Presentation Kaikoura Bypass Summary (pdf)

RIMS Forum Amplified and Updated Presentation  (pdf)

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