The following description was taken from Retrofitting of mirrors to HGVs by FTA :
The directive aims to improve the safety of road users, in particular vulnerable road users such as pedestrians, cyclists and motorcyclists. This group bears a greater risk of being involved in accidents with large goods vehicles, which have a blind spot on the passenger’s side. Legislation making an improved set of mirrors mandatory from 2007 onwards for new large goods vehicles is already in place. However, existing trucks remain in circulation without any improvement of their field of indirect vision. The new directive extends the requirements for the field of indirect vision to the existing fleet of large goods vehicles.