Slow down cars with trees. Answered
Traffic calming schemes are frequently unpopular with drivers; speed bumps and oddly-placed bollards make life uncomfortable.
In Norfolk, England, a new scheme is being presented that slows traffic without even touching the road or obstructing the driver.
Two hundred trees have been planted at the boundaries of villages suffering from speeding drivers, and it is the trees that fool drivers into slowing; they are in rows down each side of the road, and as they approach the village, they get slightly closer together, and slightly closer to the road.
Seen only in the driver's peripheral vision, the trees give the same subliminal visual clues as increasing speed would, and drivers respond by unconsciously slowing down. The illusion has slowed traffic by an average of about 3km per hour.
The illusion has been used before (rumble strips on the approaches to roundabouts are spaced more and more closely together to create an audible illusion of acceleration), but the more subtle nature of the tree-planting makes it less obvious, and thus harder to resist.
Provisionally seen as a success, more detailed, longer-term results are to be presented to the Department of Transport in the Autumn, with a view to rolling it out on B-roads nationally.