SoundPLAN (Mar 2017)

TNM 3.0 Problems from the SoundPLAN Perspective


10_PN_SoundPLAN_logoThe Federal Highway Administration has announced that the long awaited draft revision of the TNM 3.0 software will be released in the near future. We take this opportunity to document known problems that are still associated with the new software’s noise calculation core. The users of the TNM 3.0 software expect that the software is compliant with the physics and fully consistent with the written standard of TNM and free of calculation errors and random fluctuations of the results. At the moment this unfortunately is not the case.

SoundPLAN is the market leader of noise simulation and modeling software with more than 5000 licenses in worldwide use. SoundPLAN is a standards based software with over 75 standards implemented for road, railway, industry and aircraft noise. Users in the USA, Canada and other countries are interested in a fully tested version of the TNM algorithms. In the USA in particular consultants want to use SoundPLAN on Federal Aid projects and many other multiple source type projects (car wash, trucking facilities, warehouse operation, truck stops, container terminals, retail delivery, residential developments, park and ride places, stadiums) that are not co-financed by Federal dollars. It is absolutely necessary that the results for these studies deliver the same results for the road part in SoundPLAN as the noise study for the main road that may be a Federal Aid project calculated with the TNM software.

Many of these noise modeling projects involve multiple noise types such as road, railways and industrial sources and require different types of noise maps to be generated. TNM is designed for road noise only and therefore does not support comprehensive noise models with multiple noise types. So far the scope of TNM is limited to stand alone receivers, in SoundPLAN we have this option but offer various types of noise maps such as Grid Noise Maps, vertical Cross-Sectional Grid Noise Maps and Façade Noise Maps. For the assessment of noise barriers, we offer true barrier optimization for multiple receivers and also for entire neighborhoods in the form of Façade Noise Maps. Noise contours much better depict the noise situation of a project and also reveal much more about the consistency of the modeling software than the numerical results can.

Since the late 1990s, SoundPLAN has implemented the US regulations such as Stamina, TNM and the FRA railway model. For the past 17 years SoundPLAN has been working on the implementation and testing of the TNM algorithms. When we analyzed the TNM program code, we found several shortcomings and bugs in the software and notified the FHWA about them. The request from SoundPLAN and others to receive equivalency status was met with the Consistency Test Suite for the FHWA TNM. It is great to have official test questions, the master results and an acceptable margin of error to systematically test all components of the simulation.

Testing software is always best when comparing the results either directly to hand calculations based on the standards document or comparing the results to third party software. Both methods ultimately reveal systematic errors and shortcomings in the software. Mapping the numerical results in a graphic also shows where the software development traded speed for consistency of the results. With SoundPLAN we can graphically show where the TNM 3.0 software still has problems that make the results fluctuate beyond the allowed margin of error. We tested the SoundPLAN software against TNM 3.0, having access to the source code we could not only compare the results but to a limited extent also check what/if scenarios by modifying the TNM code itself. In the process of comparing results and finding the root cause of the differences, we improved the compliance of SoundPLAN but we also found mistakes in the TNM software. The errors we found in the first three chapters of the Consistency Test Suite does not allow us to continue testing the additional chapters as we cannot be certain about the cause of the deviations, known errors revealed from first three chapters or additional errors in either SoundPLAN or the original TNM software.

As an ISO 9000 certified company involved in the development of the ISO 17534 “Acoustics – Software for the calculation of sound outdoors / Quality requirements and quality assurance,” SoundPLAN GmbH is interested in supplying a fully quality tested product based on fully tested and verified standards. We also are sure that users of the TNM 3.0 expect software fully consistent with the written standard of TNM and free of calculation errors and random fluctuations of results. Known problems with the TNM calculation kernel should be rectified before users produce wrong answers. With an updated TNM 3.0 model and an updated TNM 3.0 Consistency Test Suite, we can proceed with our testing and make sure that SoundPLAN users get a fully tested and verified product. This e-mail was sent to you to raise awareness of the TNM 3.0 problems so that you can ask the FHWA and Volpe Center how TNM 3.0 results fits with the Consistency Test Suite. For a full review of the known TNM problems, please click the link below to open the PDF file.