Volkswagon has an initiative called 'fun theory' which commissions installations in the public realm.  The idea behind 'fun theory' is that designers can encourage people to change their behavior in positive ways by rewarding them with a fun experience.  This is classical behavioral psychology, but positive reinforcement turns out to be very effective tool for designers.  

Case in point:  The Piano Stairs.   

The problem: how to encourage people to take the stairs, which has obvious health benefits, rather than the escalator.  

The solution: a staircase that plays music like a piano, by turning each step into a key.  Commuters who take the stairs become performers.  The piano stairs doesn't merely react- but acts more like an interactive musical instrument, except that it engages the entire body.  The project surprises unsuspecting pedestrians with an experience that they will carry with them through out the day.  This is the power of art.