Correction by roundabouts, for acceleration and deceleration, is necessary before and after traffic lights and roundabouts. In these two cases, the equations are applied with different coefficients. To model a roundabout it is necessary to introduce a "semaphor" into each union of the roundabout with each of the roads (road objects). This results in an increase in levels depending on the distance of the receiver with the binding (not from the exact position of the traffic light object). Therefore, at the modeling level, a "semaphor" must be placed in each road union - roundabout and have the option enabled.

As regards calculation/performance itself:

CNOSSOS applies two corrections to 100 m radius from the roundabout or junction:

1. Rolling noise correction: this leads to a decrease due to low speeds before or after a cross/round. It only affects the end of rolling noise
2. Engine noise correction: this leads to an increase due to the acceleration/decolation of vehicles before and after a crossover/round. It only affects propulsion noise.

Depending on what level (wrapping or propulsion) is the most decisive, there will be an increase or decrease in total noise. For example, for a single test case (100 vehicles/hour, category 1 only, CNS_01 asphalt category, there is a speed increase below 35 km/h and a decrease above 35 km/h.

As for the minimum radius of search, 20km/h (default value) refers to the road object search radius around the traffic light object, but it has nothing to do with the calculation itself. In other words, once a road is found, there are effects due to the roundabout up to 100 m.