Practical course: Measurement of railway noise

Introduction

The assessment of noise from railway lines is based on the yearly equivalent continuous sound pressure level (Leq), evaluated separately for day (6-22) and night (22-6). Railway noise consists of single events with pauses inbetween. It is therefore beneficial to calculate the Leq values from sound exposure levels (LE or SEL) that describe the energy of a train passage and taking into account the number of events.


Sound exposure level LE or SEL und equivalent continuous sound pressure level Leq

The sound exposure level LE or SEL is determined from the time dependent sound pressure p(t) as shown below. T corresponds to the integration or event time.

The equivalent continuous sound pressure level Leq is determined from the time dependent sound pressure p(t) as shown below. T corresponds to the integration time.

If a number of ni events with a sound exposure level LEi or SELi occur in the time period of interest T, the continuous equivalent sound pressure level Leq is given as:


Measurement

The measurement took place on Mai 26 2005 near Duebendorf at a distance of 10 m from the railway line. The microphone was installed 4 m above ground. During a period of 30 minutes, A-weighted short time Leq values were recorded every second. In parallel the microphone signal was recorded on DAT for future evaluation in the laboratory (Audio example of a train passage).

Equipment in use:


Evaluation

The figure shows the measured A-weighted sound pressure level time history from 09.26 til 09.56. The corresponding data in ASCII format is found here.

During the measurement three train passages in direction Duebendorf

and three passages in direction Stettbach were observed. Obvious disturbing noise occured as follows:


Task

For the day and for the night period the equivalent continuous sound pressure level Leq of the ralway noise shall be determined. It is assumed that during the day (6-22) 200 train passages occur, during the night (22-6) 34 passages occur. It is assumed that the passages are equally distributed in both directions.

Steps:

  1. 1. For each of the six train events the corresponding event level LE or SEL shall be determined.
  2. 2. From the six LE or SEL values from 1. the average event level for each direction shall be calculated.
  3. 3. Based on the average event levels from 2. and with the number of events per day and night the Leq is calculated for the day and night period.
  4. 4. With help of a statistical evaluation of the unwanted noise during the periods without train events, the uncertainty of the above results shall be derived.


2011-06-06, Kurt Heutschi.