  We analyze the public transport networks (PTNs) of a number of major cities
of the world. While the primary network topology is defined by a set of routes
each servicing an ordered series of given stations, a number of different
neighborhood relations may be defined both for the routes and the stations. The
networks defined in this way display distinguishing properties, the most
striking being that often several routes proceed in parallel for a sequence of
stations. Other networks with real-world links like cables or neurons embedded
in two or three dimensions often show the same feature - we use the car
engineering term "harness" for such networks. Geographical data for the routes
reveal surprising self-avoiding walk (SAW) properties. We propose and simulate
an evolutionary model of PTNs based on effectively interacting SAWs that
reproduces the key features.
