The Model > The sources > Road sources > Coating / Slope / Traffic flow

Guide to different coating roads

The names of the coating roads are based on the NMPB08 and Cnossos-EU model.

Code	Description	Acoustic Effect
R1	corresponds to BBUM 0/6, BBDr 0/10, BBTM 0/6-type2, BBTM 0/6 type 1, BBTM 0/10-type2	-3.0
R2	corresponds to BBSG 0/10, BBTM 0/10-type1, BBUM 0/10 and ECF	-1.0
R3	corresponds to BBSG 0/14, BBTM 0/14, ES 6/10, BC and ES 1 0/14	+1.0
DR1, DR2, DR3	correspond to porous equivalents of these coating roads R1, R2, R3.	+1.0 / -3.0
EU-Ref	corresponds to the virtual reference for the Harmonoise, Imagine and/or CNOSSOS-EU models. This reference corresponds to a DAC 0/11 or SMA 0/11 coating, very little used in France.	0.0
Efficient two-layer draining	corresponds to a high-performance two-layer draining coating (tested for example in the Netherlands)	-3.0 / -5.0

Notes: for the surfaces DR1, R1, DR2, R2, DR3 et R3, performances may vary with the age of the coating. These variations are taken into account in the models NMPB08, Cnossos-EU and Harmonoise, but NOT in the older models.

List of abbreviations:

•BBUM = Ultra Thin Asphalt Concrete.

•BBTM = Very Thin Asphalt Concrete.

•BBDr = Porous Asphalt.

•BBSG = Dense Asphalt Concrete.

•ECF = Cold-applied Slurry Surfacing.

•BC = Cement Concrete.

•ES = Surface Dressing.

MITHRA code equivalents / NMPB-2008 classification used when converting projects from MITHRA-SIG Version 2 to Version 3 and more.

MITHRA Code	MITHRA symbol	NMPB08 Category	Averaged Age
0	ASPHALT	R2	7 years
1	POROUS	DR1	5 years
2	ASPHALT CONCRETE	R3	7 years
3	SMOOTH CONCRETE	R2	7 years
4	STRIATED CONCRETE	R3	10 years
5	COBBLES	COBBLES	10 years

Comments:

•For reference conditions (seven year old, R2 coating), both methods give the same result both on motorways and in towns. With the NMPB-2008 method, noise increases with the age of the surface and reaches a maximum at ten years. By choosing a seven year old covering we can represent the average situation which corresponds to a renewal of the road surface every ten to fifteen years.

•The 'smooth concrete' and 'asphalt' categories can be considered to be reference surfaces and naturally come under the R2 category.

•By extension, 'asphalt concrete' and 'striated concrete' can be assimilated into group R3 of the new classification.

•MITHRA only includes one porous covering. At high speed (S > 70 kph), its performance can correspond to five year old coatings in the DR1 category. Porous coverings deteriorate faster than ordinary coverings, which explains the use of a lower average age for this category.

Slope of the road

All the models take into account the slope of the road. Effect may vary depending of the model, because of the limitations imposed by the models. For exmaple, NMPB08 limits the slope to +/- 6% whereas the Cnossos-EU model limits the slope to +/- 12%.

When the user enters a value over the limits of the model, the value is automatically recalculated (i.e. minimised or maximised depending of the case) by the simulation engine.

In all cases, the slope of the road must be considered as an "average" over a sufficiently long distance and not as a localized value.

Traffic flow

All the models can use 4 types of traffic flow defined in the Guide of noise: stabilized, accelerated, decelerated, pulsated.

The NMPB08 model does not use the pulsated flow. In our implementation, this flow is simulated by using 50% of vehicles in acceleration, and 50% of vehicles in deceleration.

Code	Symbole MITHRA
Stabilized	Traffic flow with a constant speed
Decelerated	Vehicles in deceleration, until complete stop or not
Accelerated	Vehicles in acceleration, from stop or not
Pulsated	Unstable traffic with a significant proportion of vehicles accelerating or decelerating

Note: The NMPB08 model has 2 additional modes for stop and start sections when the speed is less than 25 km/h. In our implementation, the code for decelerated and stop on the one hand, and acceleration and start on the other hand are used as the same. In the simulation engine, the distribution between the different modes is made based on the speed.