# Road geometries

#### Each road is defined by a set of parameters:

- Ground impedance Z:
- the ground impedance is estimated by the Delany and Bazley one-parameter (specific airflow resistivity σ) for localy reflecting surface or by the phenomenological three parameter (resistivity σ, porisity Ω, tortuosity q2) for porous road surfaces;
- Z→∝ for a perfectly reflecting surface;
- Z(P.A.) for a porous asphalt surface (σ=10 kNsm-4, Ω=25%, q2=3.5);
- Z(grass) for a grassy ground (σ=200 kNsm-4);
- with or without an impedance discontinuity pavement/grass at d(S,disc.)=4 m from the source S;
- Note that, in the DEUFRABASE, if you choose a road geometry with a dense ground (respectively, a porous ground), you will be able to select dense pavements only (respectively, porous pavements).

- Vertical celerity profile ∂c/∂h:
- ∂c/∂h=0 for a homogeneous atmosphere (on day and evening periods, symbolized by a 'Sun' symbol on the corresponding geometries);
- ∂c/∂h=0.25 for a favorable propagation condition (rather strong effect, on night period, symbolized by a 'Moon' symbol on geometries);

- Slope:
- No slope (i.e. plane ground);
- Up-slope and Down-slope: hslope=1.5 m, θ=8°, with a sound source S at d(S,slope)=4 m from the beginning of the slope

- Noise barrier:
- No barrier;
- Barrier of height hbarrier=2 m at d(S,screen)=4 m from the source S;

- Source and receiver positions:
- The height of the source S is hS=0.05 m for all configurations;
- Depending on the configuration, the height of the receiver R is hR=1.2m, 2m or 3m;
- The distance between the source and the receiver is d(S,R)=7.5 m, 40 m, 50 m and 200 m, depending on the road configuration.

#### Road geometries currently implemented in the DEUFRABASE

(click on a figure to enlarge)