Discontinuities are characteristic leatures of the competent rock masses such as standstones and limestones, which occur in the Coal Measures of Britain and the overlying Permian and Triassic systems. The longwall method used to extract coal subjects the strata above the seam to stresses that can cause discontinuities to open or widen significantly. Unfortunately, however, the degree to which discontinuities open or gape and the behaviour of discontinuous blocks cannot be predicted.
The concept of traffic circles as a form of intersection control has been in existence since the turn of the century and is especially popular in Britain. Smaller circles have, however, not been fully exploited in South Africa. Although it has been shown that traffic circles are beneficial in terms of road-user costs, statements 'are frequently made to the effect that 'mini-circles will not work in South Africa'. A recent demonstration project in Pretoria has, however, shown that mini-circles can achieve a high degree of acceptance among motorists.