Which rules apply at a South African road race: the Cycling SA handbook or the UCI regulations?

Both, in this order. Under section 1 of the Cycling SA Road Cycling Handbook 2026:

• UCI Part 2 (Road Races) takes precedence except where the handbook explicitly provides otherwise (section 1.5).
• UCI Part 2 covers Junior, U23 and Elite men and women. The handbook adds the rules for youth categories and defines the rules for Masters (section 1.6).
• For Veteran and Masters racing, Cycling SA recognises the UCI Part 15 Cycling for All regulations (including the UCI Gran Fondo World Series). Chapter 15.5 governs all Masters events, categories and distances in South Africa, with some exceptions set out in the handbook (section 1.6.1).
• Race incident penalties use the table in UCI Part 2 (section 30.1).
• Criteriums (on a circuit closed to traffic, 800 to 10,000 m long) follow the general provisions of UCI Part 2, and the race's programme or technical guide must set out its specific rules, intermediate sprints and points (section 21).
• Stage races closely follow the regulations, including prize money, for UCI 2.2 Africa Tour events, except that international team participation isn't compulsory (section 20.1).
• The handbook binds everyone who rides, organises or officiates in road events in South Africa (section 1.2).