Glossary of terms
'A' weighting | Method of frequency weighting the electrical signal within a noise-measuring instrument to simulate the way the human ear responds to a range of acoustic frequencies |
Crossovers | Two turnouts connecting two nearby and usually parallel lines |
dB | Abbreviation for 'decibel', which is a measure of sound pressure level |
dB(A) | The 'A' denotes that the sound pressure level has been 'A-weighted' so that the scale approximates the response of the human ear. Most community noise is measured in A-weighted decibels. |
LA10 | Noise level in dB(A) exceeded for 10% of a specified time period. For a 1-hour period the level would be exceeded for 6 minutes but would be less for the remaining 54 minutes. |
LA90 | Noise level in dB(A) exceeded for 90% of a specified time period. For a 1-hour period the level would be exceeded for 54 minutes but would be less for the remaining 6 minutes. This approximates the average minimum noise level and is often referred to as the background noise level. |
LAeq | The Leq represents the average noise energy during the measurement period. When the energy level is A-weighted it may be written as LAeq. |
LAeq(1h) Day | Highest 10th percentile LAeq 1-hour measurement recorded between 7 am and 10 pm |
LAeq(1h) Night | Highest 10th percentile LAeq 1-hour measurement recorded between 10 pm and 7 am |
LAeq(15h) | Logarithmic average of the hourly LAeq measurements recorded between 7 am and 10 pm |
LAeq(24h) | Logarithmic average of the hourly LAeq measurements recorded over a 24-hour period |
LAeq(9h) | Logarithmic average of the hourly LAeq measurements recorded between 10 pm and 7 am |
LAmax | Highest noise level in dB(A) measured during the specified time period. A time response (fast, slow or impulse) must be specified. |
LApeak | Absolute highest noise level in dB(A) measured during the specified time period when time response is not used |
LDN | Day-night average sound level. An LAeq with a 10 dB(A) penalty for environmental noise occurring between 10 pm and 7 am to take account of increased annoyance at night. |
RMS | Root mean square |
Rolling stock | Railway vehicles including electric trains, locomotives, carriages, wagons, track vehicles and buffet cars |
SEL or LAE | Sound exposure level. A parameter closely related to LAeq for assessment of events (trains, aircraft, etc.) that have similar characteristics but are of different duration. The LAE value contains the same amount of acoustic energy over a 'normalised' 1-second period as the actual noise event under consideration. |
Turnouts | Assemblies of rails, switches and crossings where two tracks converge into one |
Wheel squeal | Mid- to high-frequency tonal squeal noise produced by the stick-slip action between the wheels and rails on short-radius curves |