TRAFFIC NOISE
3.1.2.4 RLS-90: Guidelines for Noise Protection at Roads

RLS-90, the Guidelines for Noise Protection at Roads (Richtlinien für den Lärmschutz an Straßen), were introduced on the national level through the General Circular Road Construction No. 8/1990 (Allgemeines Rundschreiben Straßenbau) by the Federal Transport Minister in accordance with the highest road construction authorities of the Länder.

The guidelines deal with noise protection measures and calculation methods for a quantitative representation of noise pollution. The results are also displayed in diagrams.

The purpose of these guidelines is to establish a uniform procedure. They shall help the user to consider and weigh noise protection issues in the context of road planning, to prove the necessity of noise protection measures, to develop economic and efficient solutions for noise abatement and to gear and optimize noise protection measures. The Traffic Noise Ordinance (16th Federal Immission Control Ordinance) refers to chapter 4 of RLS-90 (calculation of the rating level), which classifies RLS-90 as a legal provision for noise precaution.

Noise levels shall principally be calculated and not measured as measurements are only a snapshot of the current situation and do not convey a representative picture of the actual average noise pollution (see also further influences on measurements in section 2.4.4.2). The results of measurements mostly lie below the calculated values.

Pursuant to the guidelines, the calculations are separated into daytime (6 am to 10 pm) and nighttime (10 pm to 6 am). The sound levels apply to light wind coming from the road and they consider temperature inversions, which both leads to an increase of the sound levels.

Significantly lower sound levels can occur for bigger distances during other weather conditions. This complicates a comparison between calculated and measured levels.

The sound source is assumed at an altitude of 0.5 m above the road. In the guidelines of RLS-90, the rating level at roads is determined on the basis of traffic volume (average daily traffic volume, DTV), percentage of trucks, speed limit, type of road surface and gradient. Upward or downward slopes with gradients of more than 5 % are considered with noise additions.

In case no detailed traffic figures (day/night distribution, percentage of trucks) are available, the guidelines contain indications for various types of roads. The indications on the truck percentage are very high, i.e. that the resulting noise levels are generally too high. In order to obtain realistic results, the traffic volume should be analyzed as thoroughly as possible through several spot checks.

Note: As urban land-use planning usually treats with noise precaution, the identified traffic figures must be extrapolated to a time period of 10 to 15 years (forecast horizon). The calculation usually presumes an annual traffic growth of 1 %.

Figure 3/2 shows the dependency of the average sound level on the traffic volume and the truck percentage in a distance of 25 m from the road for a speed limit of 100 km/h (about 62 mph) in case of undisturbed sound propagation. The average distance between the ground and the connection line between place of emission and place of immission is h_m = 2.25 m (average altitude above the ground).

Figure 3/3 gives the level corrections required for different speed limits depending on the percentage of trucks.

Figure 3/4 illustrates the dependency of the noise level (sound level variations) on the distance between place of immission and sound source.

What is also taken into account is the weakening of sound through the soil and meteorological conditions as well as reflections and barriers.

Besides calculation methods, RLS-90 contain extensive diagrams for the shielding effect of walls and barriers. Figure 3/5 gives an example of the barrier attenuation (in dB(A)) of a noise protection wall at a road depending on the altitude of the place of immission above the road and on the height of the wall.

In order to determine unwanted sound reflections from noise protection walls and other reflecting surfaces, a sound level absorption of the reflected sound of only 1 dB(A) is assumed for plain building facades and of 8 dB(A) for highly absorbing noise protection walls.

Up to 3 dB(A) are added at junctions and crossings with traffic lights due to the additional noises from starting and braking – other than suggested by the above-mentioned estimation according to DIN 18005.

RLS-90 also contain calculation methods for parking area noise depending on the area, the number of parking spaces and the amount of movements per parking space and hour. They only apply to public car parks.