Case study material is used to identify some of the circumstances which will induce a favourable response to road investment. The evidence suggests that this is most likely to occur when road investment brings about a relatively large change in transport costs in an area which has under used land, a skilled mobile workforce and a competitive transport industry.The treatment of benefits accruning to agriculture in the appraisal of rural road projects has generally been poorly carried out. The basis of the forcasts tend to be weak and a failure to consider all the relevant costs of production has meant that on balance it appears that road benefits are often overvalued. Where there is some basis for predicting changes in agricultural output the World Bank's producers surplus approach is cautiously advocated. For road planning within larger regional development plans, for road maintenance and rehabilitation programmes and in situations where prediction is more difficult a minimum transport cost solution is suggested