Trail biking in the Lower Fraser Valley has become popular as an outdoor recreation activity in the last 10 to 15 years. A major attraction of this activity is the freedom it gives the trail bikers to go almost anywhere. However, with increasing urbanisation, the number of areas on which to ride trail bikes has diminished. With encroachment of residential land on still existing trail bike haunts, the number of complaints of noise, trespass, environmental damage and recreation user conflict is growing. Provision of a special use area for trail bikes has proved an acceptable solution to similar problems in other parts of North America. On the surface, it seems logical that a special use area might be equally acceptable in the study area. However, it is contended that the Lower Fraser Valley presents a different combination of social and environmental factors, and that the design of an acceptable solution to the trail bike problem requires more than mere provision of a special use area. As a methodology for designing such a solution, a model based upon 'planning under uncertainty’ is utilized. This model consists of two cycles; the 'plan-making cycle' and the 'plan implementing cycle'. The objective of the 'plan making' cycle is to design an acceptable solution to the trail bike problem in the study area. First, several aspects of the problem are explored. The demand for trail bike facilities, and how this demand has been met is examined. The problems generated by trail biking in the study area are identified and discussed. From these investigations, criteria for an acceptable solution are formulated. Four solutions are examined with respect to these criteria. These are: a) to do nothing, b) to prohibit trail bike use completely, c) to prohibit trail bike use from certain areas and d) to accommodate trail bike use. Only the latter, or a combination of prohibition and accommodation are considered acceptable. However, even if a special use area is provided, there is no basis for prediction, that it will be used, nor that it will be tolerated by the residents of the Lower Fraser Valley, nor is it known what will be the environmental consequences of such action. This uncertainty is reduced by entering the 'plan-implementing cycle'. The purpose of this cycle is to implement the chosen solution for an experimental period, and in doing so monitor aspects that have been identified as uncertain. There are four phases in this cycle» action, monitoring, analysis and evaluation. The results of the monitoring program are evaluated on the basis of how well the ‘plan’ meets the stated criteria for an acceptable solution. Evaluation will determine if the experiment should continue with modifications based on the first round of a cycle, or if a return to the plan-making cycle is required as a result of unexpected events. This model for planning under uncertainty is illustrated by describing how the plan implementing cycle could be applied in the study area. The case for choosing Eagle Ridge as the experimental site is stated and a site plan and monitoring programme is described. / Applied Science, Faculty of / Community and Regional Planning (SCARP), School of / Graduate