Samenvatting
In May 1989, an SOS system for road users in the Pretoria /Johannesburg area became operational, after 169 call- boxes were installed along 200 kilometres of major urban dual- carriageway freeways. All call- boxes are linked to a control centre by means of radio and powered by batteries charged by solar panels. The objective of this paper is to present all facets of this system, and the monitoring results which are of worldwide interest for future systems.