Visual deterrents reflect or emit light, normally red, blue or white (Figure 5.4.1) and they are typically attached to delineators located at road verges.
Reflectors which bounce the lights of approaching vehicles into the surroundings are intended to alert animals, discouraging them from entering the road or scare them away. However, studies show that such lights are not perceived by target species or are too weak compared to the simultaneously illuminated road surface, side vegetation and delineator pole itself. The effectiveness of such devices must therefore be questioned (see Rationale box. Deterrents to wildlife).
No long-term studies have so far been able to show a sustainable reduction in wildlife accidents where reflectors are deployed. In some cases, a reduction in animal vehicle accidents has been attributed not to any change in animal behaviour but to drivers cutting speed when they see reflected or emitted light, particularly blue, on the road verge. However, other studies do not show any reduction in speed.