Lack of adequate visibility at a site entrance will sometimes give rise to the suggestion that a convex mirror would address the shortcoming. However, this view is rarely reflected by a highway authority; highway engineers really really don’t like them. In addition, they are almost never sanctioned at appeal. Here is why (taken from DCS Number 400-026-333):
“The appellant would be willing to install convex mirrors opposite the appeal site to increase visibility along the lane for exiting drivers. However,” ….. “there is a risk that the use of mirrors would distort the angle of view and the distance at which vehicles travelling along the highway appeared for drivers exiting the appeal site. Furthermore, obtainable views of the mirrors could be adversely affected during inclement weather, making it difficult for drivers to safely determine whether it was safe to exit. Therefore, this form of mitigation does not adequately address my concerns relating to the safety and suitability of the proposed access.”
There is a section concerning safeguarding traffic safety at 4.1515 of DCP Online.