The Tube Challenge.

The Tube Challenge consists of visiting all stations of the London Underground in the least possible time. The competition started in 1959 and the current record was established in August 2013. This paper shows that under some simplifications, this problem and some of its variants can be cast as a Generalized Traveling Salesman Problem, as a Traveling Salesman Problem, as a Rural Postman Problem or as a Chinese Postman Problem defined on a directed graph. [ABSTRACT FROM AUTHOR]