http://maps.google.co.uk/maps?saddr=Oru ... 7&t=k&z=17
From what I could find out about the junction according to A303Chris,
I have a bit of local knowledge about this. This arrangement was put in given that the adjacent junctions on the M25, J16 and J15 are both with other motorways (M40 and M4). As it is not possible for vehicles to undertake turn rounds here, this was put in to enable emergency vehicles to turn around.
Also i have been informed by a collaegue who used to work on the gritters, that it was used for gritters to turn round so both J16 and J15 could be fully gritted.
The HA are aware of it and i have used it to get off when i am stuck on the M25. Only authorised vehicles should use it.
There is another such access point on the M40 where Fulmer Road crosses the motorway just to the west of the m25here
Regarding Palmers Moor lane, we try and potect it from any large development to ensure that the access road remains clear
(From http://www.sabre-roads.org.uk/forum/vie ... highlight=)