CRTN
The evaluation parameter in CRTN („Calculation of Road Traffic Noise“) is the level L10 (for 18 hours) in dB(A) which is defined based on the level L10 hourly in dB(A) CRTN-1988. The level L10 (1h) is the level just exceeded in 10% of the time within one hour. The L10 (18h) is the arithmetic average of all values L10 (1h) between 6:00 and 24:00 hours (total 18 values).
Emission Parameter
The emission parameter L10 is calculated from the following equations depending on what option for „Emission“ is selected:
\(L_{10}(1h)=42.2+10 \lg q\) or \(L_{18}(1h)=29.1+10 \lg Q\) in dB(A)
where the number of vehicles per hour q calculates from the 18h-count Q (see CRTN, charts 2 and 3):
\(q=10^{-\frac{13.1}{10}}*Q\) or approximately \(q=Q/20.417\).
This assumes a basic speed of v=75 km/h, a percentage of heavy vehicles (HGV) of p%=0, and a road gradient of G=0%.
Note
For the low traffic correction see CRTN.
Dialog Road (for CRTN, with emission accord. to TRL study selected)
Option „Motorway“ (marked by a red frame)
This option is displayed only if „Leq acc. to Annex A Method 1 of TRL study“ is selected on the „Road“ tab (see CRTN).
Specification of Emission
Note
Regarding splitting up the HGV emission see CRTN, Split emission of heavy vehicles over 3 sub-sources.
MDTD & Road Type
The „Mean Daily Traffic Density“ (MDTD, vehicles/24h) does not exist in CRTN as an input parameter. Nevertheless, this feature is provided by CadnaA offering two options (see list box „Road Type“ on dialog Road):
- Specification of the percentage of heavy goods vehicles (HGV, with an unladen mass > 1525 kg) in the range from 0% to 95%, applying the equation for q (as above). In this case, the resulting emission levels L10 are equal for all three daily time periods D/E/N.
Note
The attribute STRGATT enables to switch between different settings for the proportion of heavy vehicles by using the following string (where xx represents the proportion of heavy vehicles as a available from the list box „Road Type“): HGVxx (e.g. HGV50)
- Specification of one of the road types from the German road noise standard RLS-90 12354-1999. The respective data for the hourly traffic data q (veh/h) and the truck proportion p(%) is given in the next table. In this case, the hourly count q for Day calculates from the 18h-count Q as specified by CRTN while for Night the distribution in RLS-90 is used. Thus, just the daytime level is in accordance with CRTN.
| Attribute Value STRGATTNR | Road Type | Day (6-22 h) | Night (22-6 h) | ||
| q (veh/h) | p (%) | q (veh/h) | p (%) | ||
| 0 | Motorway | $q=Q/20.417$ | 25 | 0.014 Q | 45 |
| 1 | Federal Road | $q=Q/20.417$ | 20 | 0.011 Q | 20 |
| 2 | Ordinary Road | $q=Q/20.417$ | 20 | 0.008 Q | 10 |
| 3 | Local Road | $q=Q/20.417$ | 10 | 0.011 Q | 3 |
Exact Count Data
This option enables to enter hourly traffic data q and percentage of heavy vehicles p% for the three time periods Day/Evening/Night.
Note
This data can also be imported via ODBC (see Database Import (ODBC & XLSX)).
Specifying L10
The emission level L10 can be entered directly. In this case, the corrections (for speed, road type etc.) are not applied.
Diurnal Patterns
Furthermore, diurnal patterns can be used in CadnaA to specify road emission. Diurnal patterns are introduced via the local libraries on the Tables menu.
Diurnal Pattern
Subsequently, the ID of the pattern will be available from the lower end of the list box „Road Type“ on the dialog Road.
As long as the option "Use Non Standard Reference Time D/E/N" on dialog Calculation|Configuration, tab „Road“, is deactivated the data from 6 to 24 hours of the selected pattern will be used to calculate the level L10 (i.e. ignoring the traffic figures from 0 to 6 hours).
Note
In this case, the figures displayed for the hourly traffic q are not correct as they refer to the entire pattern (from 0 to 24 hours).
With counts Q being 0 (Zero) the pattern will be used as entered for calculation of emission. When entering a value for Qentered the hourly values qapplied of the pattern will be corrected according to:
\(q_{\text{applied}}=Q_{\text{entered}}(18h)*\frac{q_{\text{pattern}}}{Q_{\text{pattern,6-24h}}(18h)}\)
For the pattern above the result for L10,18h (displayed for D, while results for E and N not being relevant) will be the same when entering 18000 for Q results as with entering 0 (Zero). Entering the half amount (9000/18 h) will reduce the entire counts of the diurnal pattern to half of the values entered (see figures below).
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Example 1: road pattern „patt_01“ with 18000 veh./18 h selected, input of Q=0 considers the pattern as entered NOTE - Receiver levels may differ compared with input of Q=18000 since low traffic correction is applied with Q=0 by default (see CRTN) |
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Example 2: road pattern „patt_01“ with 18000 veh./18 h selected, input of Q=9000 considers half the amount of the pattern selected (i.e. 9000 veh./18 h) |
With the option "Use Non Standard Reference Time D/E/N" activated see CRTN.
Road & Source Geometry
According to CRTN, paragraph 4, the source of traffic noise (emitting line source) has to be taken 0.5 m above the road surface level and 3.5 m inwards from the nearside of the road’s edge (curb). This definition, however, refers to a situation with just receivers on one side of the road. In CadnaA, source lines are generated on either side of the road as the procedure should be applicable also to more complex scenarios with receivers on either side of the road or with grid calculations.
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CRTN-road with two emission lines (curb-to-curb distance 8 meters), radiation occurs just from the source line being closer to the receiver (option „Generate Rays“ activated on dialog Receiver) |
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close-up: ray is extending from the near source line, source position is 3.5 meters inwards from the road’s curb |
The distance from the source line to the curb has no influence on the emission of the road, i.e. just enabling to identify the location of the road's curb in relation to the source position. The default distance of 3.5 m is specified on the Options menu, Appearance (see Common Input Data, Specification of Road Width).
With receivers on either sides of the road both emission lines radiate.
Radiation by a CRTN-road with two receivers on either side(curb-to-curb distance 8 meters)
Additional Width
With the self screening-option activated (see Common Input Data, Dialog Geometry), the actual road width can be specified by entering an additional width > 0 m for either side of a road. The additional width overrides the additional width defined on dialog Options|Appearance. In this case the source position referring to the road‘s center line is still the same, but the curb distance deviates from the default value of 3.5 m and, thus, the total road width.
In conjunction with the option „Roads/Parking Lots are reflecting (G==0)“ activated (see Ground Absorption Tab) this affects the resulting levels.
Note
As self-screening is not treated in CRTN at all, one could conclude to not apply the self-screening option when using CRTN in CadnaA.
Example
Path: Examples\Sources\ Road\CRTN road width using add. width.cna
Example: For a road of a total width of 12 m curb-to-curb (input for „SCS/Dist. (m)“ is „w12“) and with the additional widths 5 m left and 10 m right the new road width calculates from:
source line distance: 12 - (2 x 3.5) = 5 m
source from curb, left side: 5+1.75 = 6.75 m
source from curb, right side: 10+1.75 = 11.75 m
total width curb-to-curb: 5 + 6.75 + 11.75 = 23.5 m
Speed Correction
The following speed correction applies:
\(\Delta_{pV}=33 \lg (V+40+\frac{500}{V})+10 \lg (1+\frac{5p}{V})-68.8\) dB(A)
with
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V is the road type specific traffic speed (see table 6.1 in CRTN CRTN-1988, in km/h
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p is the percentage of heavy vehicles, calculated according to: \(p=\frac{100f}{q}=\frac{100F}{Q}\)
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f is the hourly flow of heavy vehicles
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F is the 18-hour flow of heavy vehicles
Note
Despite the limitation of chart 4 in CTRN, CadnaA applies this speed correction for any speed, also below 20 km/h and above 130 km/h.
Road Surface
The following road surface types are available from the list box on dialog Road:
| Attribute ValueSTRONR | Road Surface | road surface correction ΔTD in dB at a speed of (with TD: texture depth in mm) | |
| <= 75 km/h | > 75 km/h | ||
| 0 | (manual input of attribute DSTRO) | ||
| 1 | (no correction) | 0 | 0 |
| 2 | Impervious, concrete | -1 | $\Delta_{TD}=10\lg(90*TD+30)-20 dB(A)$ |
| 3 | Impervious, bituminous | -1 | $\Delta_{TD}=10\lg(20*TD+60)-20 dB(A)$ |
| 4 | Pervious | - 3.5 | -3.5 |
Default texture depth: 5.0 mm (attribute TEXDEP)
Gradient (%)
The road gradient can be edited manually by selecting "Input (%)" or be calculated automatically from the height points of the road polygon. This feature enables for a single road to calculate the gradient correction for each road section separately (for more details see Common Input Data, Road Gradient (%)). CadnaA applies the correction according to CRTN chart 6 for positive values. Negative values lead to a correction of 0 dB:
\(\Delta_G=0.3*G dB(A)\) with gradient G > 0%
Note
Furthermore, the traffic speed V on roads with gradients has to be reduced by ΔV in accordance with CRTN, chart 5. This speed reduction is not accounted for by CadnaA automatically. Instead, always the entered speed is used for the speed correction.