London Underground with a few stations to the south of River Thames. The only London Underground stations in Zones 7 to 9 are on the Metropolitan line beyond Moor Park, outside Greater London. Some stations are in two zones, and the cheapest fare applies. Paper tickets, the contactless Oyster cards, contactless debit or credit cards and Apple Pay and Android Pay smartphones and watches can be used for travel. Single and return tickets are available in either format, but Travelcards (season tickets) for longer than a day are available only on Oyster cards. TfL introduced the Oyster card in 2003; this is
Medium-capacity rail system requisite ridership due to network inadequacies (e.g. single-tracking) or changing demographics. In contrast with most light rail systems, an MCS usually (though not always) runs on a fully grade separated exclusive right-of-way. In some cases, the distance between stations is much longer than typically found on heavy rail networks. An MCS may also be suitable for branch line connections to another mode of a heavy-capacity transportation system, such as an airport or a main route of a metro network. The definition of a medium-capacity system varies due to its non-standardization. Inconsistencies in international definitions are even reflected within individual countries.