In pedestrianised areas, some local authorities also have installed textured pathways with flat-topped bars running in the direction of travel. The idea is to guide people through busy areas and around objects by drawing them along these raised lines. For visually impaired pedestrians, they are invaluable. At London’s Old Street tube station, for example, a bright green line stretches out of the station from the ticket barriers, up the stairs, along the pavement – and right to the door of the Moorfield’s Eye Hospital.

On the roads, however, hidden messages are being used not only to guide people – but to manipulate them.

Steering drivers

In Norfolk, the county council has planted nearly 200 trees alongside the roads approaching four local villages. In recent years, the quiet, rural settlements of Martham, Mundesley, Overstrand and Horstead had found their peace being destroyed by drivers speeding along their main streets.

The trees were part of an experiment in 2010 to stop that. By planting oak, maple, birch and hornbeam on either side of the road so that the trees got gradually closer together and also nearer to the edge of the road, it created the illusion that motorists were going faster than they really were as they approached the villages – even if they kept their speed constant. In initial findings, drivers went an average of 2mph slower; accidents were cut by 20%. As the trees grow, the scheme’s proponents hope the effect will increase.