FTA/FRA
All Emissions at 0.0 m above railhead
All emission sources are placed at 0.3 m above the railhead instead of applying the sub-source heights as defined in the train class. Consequently, also the sub-source height at 0.05 m is not used.
Note
Consider that the default height of the object Railway is 0.6 m which requires to be changed to a height of 0.0 m to meet the FTA/FRA specifications.
Use non-Standard Reference Time D/E/N
In case this option is deactivated time intervals Day (D)=15 hours, Evening (E)=0 hours, and Night (N)=9 hours will be considered.
With this option activated the allocation of hours as specified on the „Reference Time“ tab will be used instead.
Note
The values displayed here are updated based on the defined time intervals DEN on the „Reference Time“ tab.
Railway Correction
This option enables to address a general correction or penalty for the receiver level:
SPLwith corr = SPLw/o corr - (Railway Correction)
In order to apply no railway correction a value of 0 dB has to be entered.
Calc maximum Pass-By-Level
The calculation of the maximum pass-by-level is not covered by FTA/FRA calculation procedures. Nevertheless, CadnaA offers to calculate this maximum level by iteration based on the Leq-based emission. The same propagation model as with Leq calculations according to FTA/FRA is used. To this end, each train class with its corresponding length is moved along the object „Railway“ according to its speed and sampling time (see below). The maximum level for this line source for each position with the specified sound power level and length is calculated.
Sampling Interval (s)
In order to determine the highest level, CadnaA shifts the source along the railway in steps based on the sampling interval (in seconds). The default value for the sampling interval is 1 second.
Option „Extrapolate trains to 1/2 length on both sides of rail“
By default, this option is activated. In this case, when calculating the maximum pass-by level, the length of each train class on the track is extrapolated by half of its length beyond the first and the last point of the drawn railway object.
By deactivating this option, the train length will not be extrapolated beyond the first and the last point of the railway object. Deactivating this option may cause a substantial level decrease for receivers/grid points near the end of the rail source and at curves (see example below).
For illustration of this effect see Nordic Prediction Method (1996).
Additional Information
Barrier Attenuation
According to the FRA/FTA-reports, the ground factor G for barrier attenuation is calculated from the effective height Heff (see figure 5-3 of the FRA-report FTA-2005 or figure 6-5 of the FTA-report FTA-2006). As this simplified concept does not work properly in complex situations CadnaA does not apply this computation scheme.
In contrary, the ground factor G for barrier attenuation is calculated using the mean height concept of ISO 9613-2 ISO-9613-2-1996 resulting in a smooth value of Aground even with complex terrain structures in conjunction with multiple obstacles in the ray's path (see ISO 9613-2, section 7.3, for details).
The barrier insertion loss Ashielding is based on the equations in table 5-1, page 5-14 of the FRA-report FTA-2005. For source types LOCO and CAR the barrier insertion loss is calculated using the equations for "propulsion sub-sources" (type PROP).
Ground Attenuation
The ground attenuation Aground for the sub-sources wheel-rail and propulsion is calculated using the equations on page 5-16 of the FRA-report FTA-2005. For source types LOCO and CAR the equations for "propulsion sub-sources" (type PROP) are applied. Aerodynamic sub-sources receive no ground attenuation at all.
Excess Shielding
The excess shielding (as of table 5-5, page 5-18, FRA-report FTA-2005) by rows of buildings (in CadnaA called "built-up areas") and by dense tree zones (in CadnaA called "foliage") are not considered - for the time being.