On-line Wall Optimization with WallDesign

Noise protection walls are very expensive, so let's optimize!

"Current construction costs are averaging $53 per square foot. This translates into a fourteen-foot high wall costing about 3.9 million dollars per mile. Construction costs for rural barriers may be lower and urban barriers may be much higher. The higher urban costs are associated with the existence of other infrastructure (like retaining wall, water pipes, etc.) that may need to be retrofitted or moved to allow the placement of barrier." (Washington State Department of Transport website)

When it costs 3.9 million dollars to construct a mile of noise barrier, it is paramount the design is optimized to get the best value for the money! SoundPLAN's Wall Design does just that!

Our most popular module because

Wall Design minimizes the wall surface area and thus minimizes the cost! Even when not all receivers can be kept below the noise limit, SoundPLAN provides answers concerning what to do.

In an off-line process, Wall Design analyzes the effectiveness of each noise barrier element for each of the receivers. Noise barriers are iterated in height and the resulting noise reduction is saved in a big matrix. When the on-line barrier selection process is started, the barrier is assembled by selecting the most effective barrier elements. As the effectiveness is ranked for each element, the suggested barrier is assembled using only the best elements. When the target noise level has been reached, the process of selecting a noise barrier can stop. If it does not reach the target value, the barrier is in the wrong place or not tall enough. If it is not possible to build the barrier taller, then some of the receivers are not properly shielded by the barrier and "passive" measures like noise control windows are needed.

What is needed to start optimizing noise barriers?

You must first generate a consistent acoustical model made up of a Digital Ground Model, the buildings that host the receivers, and the geometry where the noise barrier is proposed. Then you must shield the traffic sources.

SoundPLAN has two modes to conduct the barrier optimization - one for single receivers and one for Facade Noise Maps. The principles are the same for both, but the procedure with the Facade Noise Map has significant advantages when it comes to post processing the data. Because the Facade Noise Map generates receivers equally spaced around the buildings, the program can calculate the "facade meters" above the noise limit. If these facade lengths need noise control windows as an alternative to a noise protection wall, there are two cost structures available to find the best solution to the problem. In general, as the size of the wall goes up, the facade length above the limit goes down. As the cost of the wall increases, the cost of noise control windows decreases.

The noise protection wall to be optimized needs to be set in position before the optimization off-line calculation occurs. The wall needs to be defined as a polygon with coordinates every 10 to 50 meters. For the optimization, specify the increment height of the wall for the iteration and the maximum number of elements. The rest is just PC number crunching!

How quickly can answers be generated? How is it done?

It takes time to generate information about the effectiveness of each element of a noise barrier, especially in complicated cases such as a multiple kilometer road and a Wall Design Facade Noise Map involving 2600 receivers. For less complicated cases, the off-line pre-calculation can take seconds or just a few minutes, depending on the  situation. In a complicated case like the one to the left, the precalculation takes several hours or even overnight.

The on-line dimensioning and optimization of a noise control wall is done in seconds. The on-line part ranks barrier elements in accordance to their reduction potential per square meter for all of the receivers. The barrier itself can be considered a 2 dimensional matrix with X the element along the barrier and Z one of the panels stacked on top of each other. The on-line selection process always takes the barrier element X, Z that results in the biggest reduction of noise levels at the sum of all receivers. After an element is chosen, the noise levels at the receivers drop. If the receiver is below the design goal, it does not contribute to the selection of the next barrier element. The selection of barrier elements X, Z goes on until all the receivers are satisfied or there are no more elements to be selected.

The step by step selection of elements for optimizing the noise barrier is recorded in a histogram. This Optimization History shows where no additional benefits would be gained from making the wall taller or longer. The number of inhabitants above the noise limits does not decrease below 48!

The Cost Comparison between the noise protection wall and the cost of window upgrades supports the decision to build a wall to a specified height and not higher. The red vertical line shows this cutoff point. It is user controlled and will result in an immediate answer in tabular form of the noise levels for all receivers. When the wall is saved, the optimized form and the red line are also saved to be used in other noise maps such as Grid Noise Maps, from which SoundPLAN generates Difference Maps showing differences between the before and the after scenarios.

Not all barriers can be designed straight forward using the automatic process. Sometimes designers do not want the gap between elements or they want to limit the wall height in a certain area. The user can control the barrier manually and see the results instantly in the graphics window in 2D or 3D. Other instant answers are the cost of the noise barrier, the total surface area and the effect of the design change upon the noise levels at the receivers.

 

How can efficiency and cost effectiveness be managed?

If a noise barrier can satisfy the needs of all residents without having excessive height and length, Wall Design solves the problem directly. But this is not always the case.  Some buildings may not be properly shielded with the noise barrier, and may require noise protection windows. It is often more economical to use a combination of a noise barrier with noise control windows rather than just using the barrier.

If the basis of a Wall Design calculation was a Facade Noise Map, the program knows the cumulative number of meters of facades above the noise limit. If we assume a certain cost to upgrade noise control windows per facade meter, the program can compare the cost of the noise protection wall to the cost of noise control windows. In general, when the cost of the wall goes up, the length of unshielded facades goes down. The cumulative cost may show a point where extending the noise protection wall increases the cost but not the benefits.

Noise protection structures are designed to keep the noise levels below the limit and to have a good cost-benefit ratio. Both objectives raise questions: Shall noise limits be observed for all dwellings? Is the noise protection wall justified if the noise levels are below the limit for the ground floor only? How can one assess the benefit?

In 2006, the Swiss Federal Bureau for Environment (Bundes Amt für Umwelt - BAFU) documented a well practiced method for creating a diagram showing the effectiveness and efficiency of a measure. Efficiency means a good relationship between cost and benefit. Effectiveness is shown when goals such as fulfilling target values are reached. Both properties generate the WTI and are necessary for a successfully designed wall.

The cost of a noise protection wall includes the real estate cost for the land where the wall will be built, as well as construction and maintenance costs. The benefit is lowering the noise levels, which increases the real estate rental price. The loss of rental income is used as the sole factor in a dB/rental price model established for Switzerland that has also proven useful in other countries. The effectiveness is the ratio of apartments above the limit before and after erection of the noise protection wall.

A WTI measure is viewed most positively if it is both highly effective and highly efficient. Noise protection walls built where there is minimal infringement of the noise limit show only marginal improvement in terms of dB values, so are rated with good effectiveness but bad efficiency. Noise protection walls that yield big noise level reductions but still don't satisfy the the noise requirements, have good efficiency but bad effectiveness. It is clearly best to have high marks in both areas.

Surely the evaluation of noise protection structures could use other parameters and include the cost of noise in the health care system or questions of urban design. In practice, maximizing the WTI index has proven valuable in many studies in Europe. The procedures are transparent, traceable and repeatable. It is important, however, that the calculation area  is large enough that all positive effects of the measure are brought into the evaluation. It is also paramount that noise levels are calculated for all facades and all floors of all residential buildings in the study area.

The WTI in SoundPLAN is evaluated automatically using the building footprint, the renting price without noise, the decay of rental income due to excessive noise, and the applicable noise limit for the buildings.

 

 

TNM*, NMPB, CoRTN, RLS 90, NMPB, RMR2002, CoRRN, ISO9613, Nord2000, Schall03, Kilde130.......

As the pre-calculation of SoundPLAN for Wall Design uses the standard calculation facilities, there is no limit SoundPLAN Wall Design works with all standards for outside noise propagation -road noise, railway noise- industry noise (except the WDI calculation method).

Under normal circumstances walls are the preferred method of controlling transportation noise, on the left see a list of standards supported.

 

 

 

 

 

 

* TNM is a registered trademark of the US government. SoundPLAN's implementation of the TNM rules and regulations has not been tested, evaluated, or approved for use by any Agency of the United States Government.

Barriers and Berms

Wall Design is used for vertical walls and berms. For walls, you can define the absorption coefficients for the side facing the road and the side away from the noise source.

Can I continue working with a designed noise barrier?

The noise barrier resulting from a Wall Design optimization can be saved as a SoundPLAN Geo-File and can be included in any calculation so a Grid Noise Map can show the before and after scenario and difference maps can depict the improvements in 2D or 3D.

The Facade Noise Map to the left shows buildings painted in accordance to the highest noise levels found on that building. The scale is part of the graphic.

What are the limitations?

The Wall Design optimization works only when one noise barrier that is being optimized is between the source and the receivers. It requires two calculations to optimize a barrier on the median of a divided highway and a barrier at the edge of the road.  First optimize the median barrier, reducing 3dB from the noise limit goal. Save the median barrier and then re-run the calculations with both directional lanes in place, the already designed median barrier and the proposed barrier at the edge of the road. For the on-line part, run the optimization aiming for the final noise limit you want to attain. This two step process gets around the limitation of not being able to optimize two barriers at the same time.

SoundPLAN also has a geometric limit. If a vertical barrier has extra non-vertical elements, no optimization is possible. For this case, we recommend to optimizing the barrier as  a straight barrier and then using this information to introduce curved barrier elements. A re-calculation is paramount in this case.

Wall Design is a 100% solution for straight barriers only. If you use berms as design elements and optimize them with Wall Design, remember not only the height of the barrier changes but also the location, so it is sometimes the "neighboring" element also in the path that may be responsible for some of the shielding. It is paramount when designing berms that after optimization a re-calculation confirms the findings.

Copyright 2014 SoundPLAN international LLC, Shelton, WA 98584, USA