A fundamental principle of international road geometric design guidelines and handbooks is that along a roadway, the available sight distance should be sufficient to enable a driver, travelling at a reasonable speed, to stop before reaching a stationary object on his path. It is generally recognised that this required stopping sight distance depends on human, vehicle, highway and environmental factors and its estimation is a complicated issue. Therefore, in most road geometric design guidelines worldwide, the mathematical models used for estimation of the required stopping sight distance have been revised several times. The objective of this paper is to review, analyse and compare the changes that have occurred over the years in the models used for estimating required stopping sight distance in German, American and Australian guidelines for the geometric design of rural roads, and to examine relevant human factor aspects that have not yet been sufficiently incorporated into design guidelines.