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CRTN

Calculation

Select the evaluation parameter from the list box:

  • L10: This option evaluates the L10 level according to CRTN (default).
  • Leq acc. to Annex A Method 1 of TRL study: The conversion rules according to method 1 of TRL study are applied (using equations (4.4) and (4.5) of TRL-2002). The conversion is based on the same segmentation rules as being used for L10 calculations.Since the conversion for non-motorways with hourly traffic flows < 200 veh/h and during the period 24:00 to 06:00 hours deviates (see equation (4.5) of TRL-2002) note the following points:
    • A further check-box „Motorway“ is displayed on the dialog Road (see CRTN) enabling to distinguish between motorways and non-motorways.
    • Allocate the period 24:00 to 06:00 hours to the nighttime by typing in 6 letters N (see Reference Time Tab). Note that just the hourly traffic from 24:00 to 06:00 hours having N's is taken (when using diurnal patterns).
    • The configuration of calculation shows an additional checkbox to „use formula 4.5 up to 30m only“.
  • Leq = L10 - 3.0 dB: This approach to evaluate Leq from L10 is used in Australia.

Note

In order to apply Annex A Method 3 of TRL study TRL-2002 to noise grids and receivers see chapters Grid Arithmetic and Editing the Result Table.

Use Non Standard Reference Time D/E/N = 12/4/8

When using diurnal patterns the hourly traffic flow considered to calculate the emission is by default restricted to the time interval from 6:00 to 24:00 hours. To apply the daily hours as allocated to the intervals D/E/N on the „Reference Time“ tab this option has to be activated.

Note

The application of diurnal patterns with this option deactivated (i.e. strictly applying CRTN) is explained in chapter CRTN.

Example

In this example, the daily intervals D/E/N are set to D from 4 to 18 hours (14 hours), to E from 18 to 22 hours (=4 hours), and to N from 22 to 4 hours (= 6 hours).

Dialog Calculation|Configuration, „Reference Time“ tab

The following diurnal pattern „patt_01“ is used in this example. Traffic figures are 200 vehicles/h from 0:00 to 6:00 hours, and 1000 vehicles/h from 6:00 to 24:00 hours (with HGV=20% for each hour).

Diurnal Pattern „patt_01“

The hourly traffic data for periods D/E/N result from (see dialogs below):

for D: 12400 veh/14 h = 885.71 veh/h

for E: 4000 veh/4 h = 1000 veh/h

for N: 2800 veh/6 h = 466.67 veh/h

The figure to be entered to normalize to a different total traffic count Q still refers to the traffic counts within the time interval from 6:00 to 24:00 hours (i.e. 18 hours) of the pattern selected.

Example 1:
diurnal pattern PATT_01 with Q=0 veh/18 h (6-24h)
applies full traffic counts as from selected diurnal pattern
Example 2:
diurnal pattern PATT_01 with Q=9000 veh/18 h (6-24h)
applies - in this example - 50% of the traffic counts from the selected diurnal pattern
(so, not entering 50% of 19200 veh/24h = 9600 veh/24h

Use Low Traffic-Correction K

Clause 30 of CRTN specifies that for a road segment where the traffic flow is in the range 50<=q<200 veh/h or 1000<=Q<4000 veh/18h and the shortest slant distance d' source-receiver is less than 30 metres a low traffic-correction shall be applied. The low traffic-correction K is calculated according to chart 12 of CRTN.

In CadnaA, the conditions for q (attributes MT, ME, MN) or Q (attribute DTV) are checked depending on what is selected. The low traffic-correction is applied to all receivers or grid points meeting the conditions.

Note

The emission value L10 displayed on the dialog Road, however, does not include the low traffic-correction as the receiver's distance is not available for a road object.

In CadnaA, for traffic flows lower than the lower limit the following is applied:

  • q<50 veh/h: K=K(q=50 veh/h)
  • Q<1000 veh/18h: K=K(1000 veh/18h)

Note

The restriction in CRTN, clause 30, that „otherwise no correction should be applied“ is, therefore, not respected for values q or Q smaller than the respective lower limit. On the other hand, this strategy avoids, for example, the emission level to increase for q=49 veh/h compared with q=50 veh/h when not applying such a strategy.

Reflection via Correction (1.5 dB), NOT via mirror sources

CRTN clause 26.2 specifies that the reflection from buildings or other reflecting objects (e.g. barriers) on the opposite side of the road have to be considered by a correction of 1.5 dB depending on the angle of the reflecting object/s seen from the receiver. The value of 1.5 dB occurs in case the entire length of the road has reflecting buildings (i.e. is the maximum reflection correction).

When activating this option this CRTN-specific reflection correction of +1.5 dB is applied. CadnaA considers the sum of angles of reflection in relation to the total segment angle as specified in figure 5 of CRTN.

long road with opposite reflecting barrier,
reflecting barrier deactivated
reflecting barrier activated,
calculation of reflections according to CRTN clause 26.2
Note - Level increase is just 1.4 dB due to finite road & barrier length.

With this option being deactivated, the increase due to reflections is calculated by mirror sources (as usually with CadnaA). In this case, the settings on „Reflection“ tab apply (e.g. order of reflection etc.).

Note

Buildings/barriers should be set to reflective for reflections to be included.

Reflected rays by a barrier (1st order of reflection)

However, the results with this option deactivated are not in line with the specifications of CRTN.

Note

Buildings and barriers with an absorption coefficient of less than 0.8 will be accounted for as being reflecting in CRTN calculations where the max. 1.5 dB correction applies. Buildings and barriers with an absorption coefficient larger or equal to 0.8 will be excluded from the 1.5 dB-correction.

Calc accord. to "Design Manual for Roads and Bridges (DMRB)"

The "Design Manual for Roads and Bridges" (release August 2008 DRMB-2008) states the following modifications to CRTN-calculation:

  • road surface correction editable (attribute DSTRO),
  • no further increase of ground absorption beyond 600 m distance from the road (Agr=Agr(600 m) for d>600 m),
  • additional rules whether reflections from opposite facades or barriers occur.

With this option activated the DMRB-calculation rules are applied.

Note

The option "Reflection via Correction (1.5 dB), NOT via mirror sources" needs to be activated in this case.

Split emission of heavy vehicles over 3 sub-sources

Australia modifies the CRTN calculation model by applying three different sub-source heights just for heavy vehicles (HGV). Activating this option enables to specify:

  • the emission heights for up to tree sub-sources (in m) and
  • the Delta-values (in dB) for the sub-sources in relation to the overall emission of heavy vehicles (HGV).

The default values are -4.77 dB, since -104.77/10=10 lg (1/3), assuming that the overall energy is distributed evenly across all three heights. The double arrows (>>) offer access the object specific attributes which can be used to specify a numerical expression.

Option „Normalized“

Activating this option ensures that, whatever values or expressions are entered, the energy fractions get normalized to the sum representing 100%.

Additional Information

Facade Effect

CRTN specifies in clause 26.1 that for calculations of the noise level at a distance of 1 metre in front of a façade a correction of +2.5 dB has to be made. CadnaA does not apply this correction automatically for the time being as this CRTN-specification does not match the normal approach when calculating façade reflections.

By default, the façade level at receiver points in front of the façade (e.g. at 0.05 m off the facades plane) does not include reflections at the own buildings surface. This is achieved in CadnaA by setting the "Minimum Distance Receiver-Reflector" to e.g. 1 m (so, larger than the distance of the receiver from the façade).

Reflections are calculated when this distance is set to 0 m, when the building is reflective, and when at least the first reflection order has been selected (Configuration dialog, „Reflection“ tab). To apply the correction of 2.5 dB for CRTN-calculation the following conditions have to be fulfilled:

  • The option "Reflection via Correction …" on the „Road“ tab of the dialog Configuration is activated.
  • Each receiver intended to consider the CRTN-correction of +2.5 dB has the text-variable FACADE=1 specified on the receivers memo window.

The building below has got two receivers attached to its facade.

Two receivers at building’s facade, left rcvr with correction, right rcvr w/o

The receiver on the left has a string variable FACADE=1 defined. The increase of 2.5 dB according to CRTN is considered. The receiver on the right has no text variable defined (or with the text variable being zero, FACADE=0). Thus, the level increase is not added.

Grid calculations for EU-noise indices

see Grid Arithmetic, Grid calculations for EU-noise indices with CRTN

Conversion to EU-indices at individual receivers

see Editing the Result Table, Conversion to EU-indices at individual receivers with CRTN / TRL