PPS 8 Open Space Sport and Outdoor Recreation·Page 21·5.16
Calculating useable open space provision
Only open space with demonstrable recreational or amenity value counts toward required provision; highway verges and visibility splays are not normally counted.
In calculating the precise amount of public open space provision needed in an individual development proposal, only space of demonstrable recreational or amenity value i.e. 'useable' open space, will generally be counted. Accordingly, verges and visibility splays, which form part of the adopted highway, will not normally count towards the open space provision.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/PPS 8 - Open Space Sport and Outdoor Recreation.pdf