Two colour schemes – black on white/silver or white/silver on black – are provided to allow for varying external or internal circumstances.

One interesting aspect of the sign development was the review, selection and, in some instances, design of pictograms for use in the sign system. In order to ensure that the signs communicated with as wide an audience as possible, pictograms were tested for their effectiveness using a group of 10 participants whose first language was one other than English.

The pictogram that was least recognised was “No Entry” – despite it being used nationally on traffic control signs. Another that scored poorly was the US Department of Transport “Baby Change” pictogram. This was redesigned to incorporate a carer with an infant.