*Calculation of Road Traffic Noise (CRTN) states that is unreliable in situations where flows are less than 50 vehicles per hour. How should traffic flows on a waste disposal site be modelled when they are this low?*

CRTN is based on the L_{A10} value, i.e. the noise level exceeded for 10 % of the time. When flows are very low, vehicle noise may not be present at significant levels for 10 % of the time, in which case the L_{A10} is more a function of the ambient level than of the traffic noise. This is probably the case at 50 veh/h which is less than one vehicle per minute.

Here, you would be advised to use the ‘haul road’ calculation of BS5228, given in the ‘SiteNoise’ module of NoiseMap, which provides the L_{Aeq} of the source. This calculates the contribution of sound energy from each moving point source, so is applicable to *any* flow rate and speed, as long as you have the sound power level or L_{Amax} at 10 metres for the applicable vehicle speed.

This will give an appropriate calculation of the L_{Aeq} values. As previously noted, L_{A10} is probably not the most appropriate index to use in these situations.