The concept of encumbered space is recognized and defined. The components and their subcomponents are identified and isolated. The relative interactions between them are noted. Initial families of velocity-clearance curves for several haulage media are derived, noting the vital need for future research. The basic assumption that production is proportional to the product of capacity and velocity is utilized and the concept of derating the maximum theoretical production rate of an underground mining situation to obtain a more realistic estimate of the actual production rate is introduced. An example of the use of derating factors (derived from the results of questionnaires) in obtaining an estimate of production is presented. An order of magnitude check is made on the weighting of the initially selected derating factors. Results proved to be consistent, confirming the approach. Recommendations for future research are made.