Yes in daylight, no after dark — and the risk sits almost entirely on the Baden Powell Drive section across the Cape Flats, not on the Stellenbosch end.
Where it runs. The R310 starts in Stellenbosch, runs west past Vlottenburg and the Spier and Meerlust estates, crosses the N2 near Macassar and then continues as Baden Powell Drive along the False Bay coast toward Muizenberg and Strandfontein. Most visitors meet it in two very different halves: the winelands half between Stellenbosch and the N2, and the coastal Cape Flats half beyond it.
Which stretch carries the risk. The Baden Powell section between the N2 crossing and Strandfontein is the one that generates the warnings. It is a fast, largely unlit road running past informal settlements with easy pedestrian access to the verges, and it has a long-standing pattern of stone-throwing at vehicles, staged obstructions and opportunistic robbery at standstill traffic. Almost all reported incidents cluster at dusk and after dark. The Stellenbosch-side half, by contrast, is a conventional agricultural road with steady traffic, farm entrances and speed enforcement — its real hazards are pedestrians, tractors and drivers leaving tastings.
When it is fine. Between roughly 07:00 and 16:30 the whole R310 is an ordinary drive and thousands of commuters use it daily. Keep windows up and doors locked, keep bags in the boot rather than on the seat, leave space at intersections so you are never boxed in, and do not stop for anyone flagging you down or for debris placed in the lane — drive around it if it is safe to do so and continue to a petrol station. From late afternoon onward, treat the Baden Powell half as closed to you.
The safer alternative. For Stellenbosch to Cape Town, stay on the R310 only as far as the N1 or N2 and do the long leg on the highway: R310 to the N1 at exit 39 and in via the N1, or R310 to the N2 westbound. Either adds roughly 5 to 15 minutes over the coastal shortcut, which is a small price for a lit, patrolled, busy dual carriageway. If you want the coastal drive itself, do the M3 and Boyes Drive through Muizenberg instead — same views, far busier road.