Calculation of ROAD traffic noise.
*CALCULATION ROAD TRAFFIC NOISE*
This script computes the noise level in dB(A) at a given distance from a road. Important data are the number of cars and trucks that use the road, the mean speed and the distance from you to the road. Emission data according to the 2002 version of the Dutch calculation method.
- vans: delivery trucks, all types of buses.
- heavy vehicles: all trucks that have more then 2 axles or have more then 2 tyres on any of the axes, except buses.
The mean speeds for each of these categoriesNote that the real, mean speed per vehicle categorie has to be filled in; not the permitted maximum speed!
(default speed is in km/hr; check the button if you want to express speed in miles per hour)
The road surfaces:
- Smooth asphalt
- Concrete/asphalt mixtures
- Paved (bricks)
- Regular porous, sound absorbing asphalt
This is the kind that reduces noise by approximately 2 dB(A) at higher speeds (over 70 km/hr) and lorries below 30%.
- Special sound absorbing road surfaces . Still in developement are high performance sound absorbing road surfaces. See the special section on this topic. Reduction is set at -5 dB(A). Somewhat optimistic, but achievable.
Distance to observerIn meters, like all distances. This is the horizontal shortest distance between the calculation point and the center of the road. Slant distances are calculated internally.
If someone asks, I will add a conversion to from/feet. It adds some overhead, so I prefer not to. The option to use miles is an experiment to see if this works. It does.
Distance to intersectionIntersections produce generally more noise then free flowing traffic. Only when the crossing road is of a very low order, you may ignore this. A value of "0" is interpreted as no intersection present. This is the default. Distance over 150 meters have no effect.
Reflection from other sideSound reflected back from the other side adds to the total sound load. To correct for this properly, the heigth, distance and "openess" of the structure opposite is needed. A totally closed surface (large appartment block) get a reflecting factor of 1.
Angle of sightStandard is 127 degrees. When the view on the road is impeded by an obstacle of sufficient height, the remaining angle may be filled in. Eg, if half the view of the road is obstructed (by a high enough obstacle), fill in 63 degrees.
height of observer (default is 5 meter)
height of road (default is 0 meter)
Absorbing fractionfraction of soil that acoustically hard, as opposed to absorbing.
0=totally hard, 1=entirely absorbing. Inputs larger then 1 are interpreted as percentages and converted accordingly.
Absorbing soils are grass, forest floor or arable land, also snow. In the case of snow you may have to correct for the time the snowcover is present. Default value is 0 (city street). At larger distances some absorption is likely. When attempting to find the distance where a sound level occurs, an assumption is made, depending on distance.
The maximum amount of absorption is around 4 dB(A).
Estimate distance for a given noise level
There is no direct relationship between noise level and distance. However, fill in the desired noise level in the noise level-box, and the script iterates until it finds a distance which gives a reasonable approximation to the desired level. Usually within 0.1 dB(A). On my machine the respons is immediate, and I suppose that on any machine capable of handling Netscape this will be the case.
Page from 15 februari 1998