4.1 General 4.1.1. Signs to diagrams 516 (S2‑2‑13, see Figure 4-1) or 517 (S2‑2‑14, see Figure 4-2) should be used where a reduction in width on a single carriageway road presents a hazard. Dual carriageway situations are dealt with in 4.1.6. Signs will not normally be needed if the narrowing does not result in the loss of a lane and involves a taper no more severe than indicated in Table 4-1. However, signs should be provided regardless of the rate of taper where a lane is lost on a single carriageway road or where the reduction in width is so great that the centre line marking has to be omitted (see also 4.1.4). The “REDUCE SPEED NOW” plate (see Figure 2-9 & 2.4.2) should be used if a significant speed reduction is advisable. These signs must not be used to warn of the termination of a dual carriageway (see 5.1).