[tedunangst]

What makes it intricate? There's a big table of station x station fares. Filling the diagonal with $6 is no more complicated than filling it with $0.

[sowbug]

You're thinking from an implementor's perspective. From the customer's perspective, it's a weird nonlinear pricing model that charges you more to be taken a shorter distance. Honest people who forgot their keys at home or whatever and need to run back home have to deal with the nonlinearity.