Idea of the Day ... on Changing Behaviour through Design

In Belgium and the Netherlands they have put large butterfly nets along the cycle paths to encourage people to throw their litter in the right place rather than littering just anywhere. This design is based on a technique called 'Nudge' which uses people's nature/instinctive behaviours as the starting point of any design.

 
Nudge Theory too is used to design care homes for people with Dementia, in highways design and putting low-cost gym equipment in parks.

How else could we use 'nudge' for the benefit of the wider community?