Abstract :
The author shows that relay interlockings can be produced and used cost effectively. Of all the interlocking techniques available in South Africa, the optimized, geographic relay interlocking is still the cheapest. The principle of open tender amongst the railway signalling contractors will always apply for the supply of interlockings and, until the prices and cost of maintenance of other types of interlocking prove their cost effectiveness, relay based interlockings will be utilized
