Street design and urban canopy layer climate

Planning is always involved in making choices between alternatives. In the case of designing for street climate the objectives may be mutually exclusive. For example, whilst open geometry is conducive to air pollution dispersion and solar access, a more densely clustered arrangement is favourable for shelter and energy conservation. This dilemma is investigated by reviewing the results of recent urban canyon field studies and of scale and mathematical modelling. By concentrating on quantifiable relations it appears that it may be possible to find a range of canyon geometries that are compatible with the apparently conflicting design objectives of mid-latitude cities. If this is correct, traditional European urban forms are climatically more favourable than more modern, especially North American, ones.