RYNO Motors' single-wheeled electric scooter is self-balancing, has a turning radius of zero when stopped, and only takes up about as much space as a folding bicycle -- so it's conceivable that commuters could bring one onto a train.
Pinner wrote: That third one down. that piece (the original at least) was the first artwork we looked at in my very first art history class. Art started as paint on the walls. (I wish I could see these art pieces in person.