Noise investigations explained

When local and other authorities make a request for a noise investigation they usually mean a rail and road traffic noise investigation. This is a method of examining noise levels on property, at the façade of a building and even noise indoors.

The reason the investigation is required is the fact that noise can adversely affect people’s health. It is advantageous to know in advance if a noise situation will have a negative effect on you, your neighbours’ or colleagues’ health. The other reason is to check whether additional measures are needed in order to fulfill building regulations, indoor noise regulations and industrial noise regulations.

An investigation comprises a diverse range of measured and predicted information for railway traffic and road traffic. It can even include an investigation of industrial noise or technical equipment such as fans if they are to be found in the area.

How one measures and calculates traffic quantities takes different forms. Most often, road and rail traffic noise is not measured, it is predicted using computer simulations. A map is drawn in a custom software which is used to calculate the propagation of sound over property and on buildings. After elements such as height contours, ground types, roads, railways, buildings etc. are added to the model, simulations can be run which show the predicted noise levels in 2D and 3D.

3D noise mapping

Source data for rail traffic quantities comes from Travikverket’s (Traffic authorities) planning documents for rail traffic and their predictions for the year 2040. Detailed information is available such as track number, number of trains, train types (including acoustical data), average length and their speed.

Source data for road traffic quantities is based on the so called ÅDT – annual average daily traffic. The traffic authorities estimate the ÅDT for the state governed road network and local authorities estimate the remaining roads. There is a detailed explanation of how the estimation is performed on Trafikverkets website (see link below). The number of vehicles, their speed and the proportion of heavy vehicles forms the basis for a computer simulation. (in Swedish)

Local authorities most often carry out short period tests using tube sensors (see picture below). The number of vehicle axels that cross the tube is counted and statistical analysis allows the estimation of the ÅDT.

Local authorities measure traffic quantities with tube sensors. Photograp: Steven Liddle

Industrial noise, on the other hand, is most commonly measured at a nearby façade. It is sometimes difficult to separate the noise from an offending piece of equipment when there are several other fans and cooling devices in a courtyard or on a roof, for example. In this case, noise investigations via computer simulation can also be used.  Source data for a single source can be derived from measurements made close to the offending device or from equipment data sheets which describe the sound power levels. It is then possible to predict the propagation of noise at nearby buildings.

Sound levels in a point array on a facade