Partial enclosures have been used for the control of road traffic noise in Europe and have been considered for some road projects in Australia. However, the Calculation of Road Traffic Noise (CRTN) method has no algorithms for estimating the insertion loss of partial enclosures. In particular, CRTN does not consider the effect of multiple reflections within the enclosure. Also, environmental noise modelling software packages cannot always estimate the barrier attenuation as the edge of the enclosure is not necessarily between the noise source line and the receiver. This paper describes a simple modification to CRTN that can be implemented in a software package such as SoundPLAN which estimates effects. The risks associated with such a simple modification are estimated.