Smart Motorway gantry sign
A gantry structure spanning the motorway with electronic signals, blue signs showing an exit and the following text.
Exit destinations: A404 Amersham, Ch'wood; Rickmansworth .
Forward destinations: (M40, M4), Oxford; Heathrow [Airport symbol] Gatwick [Airport symbol] M25 .
Junction number: 18.
A very small junction serving a small number of local destinations. This is the sort of place you live if your lifestyle will support golf course memberships, private school fees and the house price premium that comes with direct access to the M25.