John MacDonald

Comparison of Measured and Modeled Sound Levels in the Vicinity of Traffic Noise Barriers

A detailed noise prediction model was used to compare 11 highway noise barrier locations in Florida. Insertion losses, ground effects, shadow zones, and overall trends were determined or analyzed, or both. Each location was modeled using STAMINA2.0 (current FHWA regulatory model), STAMINA2.1 (Florida’s version of STAMINA2.0 with state-specific emission levels), the Traffic Noise Model (often referred to as TNM; this model will replace STAMINA2.0 in the year 2002), and the University of Central Florida Community Noise Model (CNM5.0). The modeled results were then statistically compared with the measured results. Statistical evaluation results were similar for all models for overall, absolute prediction compared with the measured value, with STAMINA2.1 being slightly better. All models provided adequate results, but ranges of error were significant. When the propagation components were explored, by comparing reference levels with those behind the barrier, the TNM was significantly better. The results also provided further insight into the benefited regions behind the barrier, a more detailed understanding of how the models perform for this complex interaction with the ground and sound wave, and how background levels change the actual size and shape of the benefited region.

Method To Determine Reasonableness and Feasibility of Noise Abatement at Special Use Locations

Most states have policies in place that determine whether noise abatement is necessary and reasonable/feasible for Type I projects. These policies mirror federal guidance and apply to various land uses near the proposed project. Special land use facilities such as parks, churches, and schools are included in the policy as far as when abatement may be necessary (i.e., FHWA noise abatement criteria), but the determination of whether the abatement is reasonable or feasible may not be adequately addressed. A survey of state Departments of Transportation (DOTs) indicated that states are dealing with this need for reasonable/feasible determination for special land uses but do not have formal policies in place to address the issue. A systematic procedure would eliminate arbitrary decisions. A methodology developed for the Florida DOT to aid in the development of a procedure for special land use cases is presented. This methodology includes a feasibility flowchart that leads an individual through the process of determining whether abatement at a special land use site is feasible. The feasibility flowchart directs the individual to cease analysis because abatement is not feasible or to continue onto a reasonableness worksheet that determines whether abatement at the site is reasonable. The reasonableness worksheet leads the individual through site-specific calculations to derive an “abatement cost factor” used to determine reasonableness of abatement at the site.

The University of Central Florida Rail Noise Model

The Railway Noise Model (RNM) is a point source simulation model using a Windows‐based program written in Visual Basic. Locomotives and rail cars are input by the laser using a graphical interface. The interface allows spreadsheet‐type format or the user may use the mouse to drag and drop railroad tracks and barriers and to place receivers. The model has the ability to model heavy rail and light rail locomotives and rail cars. The user can observe defined trains moving along the railroad tracks to check input. Leq sound levels are calculated and reported during the simulation and then tabulated at the conclusion of simulation. The algorithms of the RNM follow the U.S. Federal Transit Authority Noise and Vibration Impact Assessment (DOT‐T‐95‐16) guidelines. The Railway Noise Model uses Lmax passby levels from REMEL curves to compute sound levels. The RNM simulates a 24‐h period of rail traffic and computes Ldn, Lmax, SEL, and Leq levels at the receivers. Testing has shown that the RNM results match those o...

The University of Central Florida Community Noise Model

The Community Noise Model (CNM) is a true simulation model written in Visual Basic allowing modeling of motor vehicles. User input is simplified by permitting spreadsheet input or graphical input using a mouse. Due to its simulation nature, the model handles interrupted flow traffic much better than conventional line source models. The model begins by using reference energy mean emission levels (REMELS) from a quite extensive measurement program. Propagation characteristics (geometric spreading, ground effects, atmospheric absorption, diffraction, etc.) are calculated at user‐specified time step and energy is summed at user‐defined locations. Using the acoustic energy summations, the model reports Leq, Lmax, and statistical levels. Traffic parameters are also reported. Validation has been performed as well as comparison to other established models and will be presented. The CNM performed quite well and at intersections outperformed other models when comparisons were done to measured data.