When given the choice to ride a bike or to take the Metro (rail or bus), I would love to be able to choose the bike every single time. But, the reality of living in a city like DC (and most cities across the country) is that sometimes combining methods of transportation is necessary to make it to ones destination within a reasonable amount of time. Fortunately, some cities have very bicycle-friendly public transportation options, which make a multifaceted approach to commuting possible.The District of Columbia is a fairly expansive city, and the DC Metro area includes portions of Northern Virginia and Maryland. Although I can think of worse rush hours, traffic in DC can be unpleasant. The good news is that it is relatively easy to ride a bike from a neighborhood in Arlington, VA to one of the many Metro stations in the area, where there is ample bike parking (even secure bike lockers, in some instances) for people that can use the Metro to get to their final destination. For people that want to take their bikes onboard, they need to plan their trips around rush hour (weekdays from 7-10am and 4-7pm), holidays and special events. Getting a bicycle onto the Metro is not difficult- just do not attempt to transport your bike on an escalator or to enter a Metrorail car through the center door (trust me- theyre watching). Metrobus is a good option for people that need to move a bike during rush hour; the front of every bus has a rack capable of holding two bikes.Plenty of other cities have made accommodations for multi-mode travelers, but sometimes understanding the rules of riding can be a slightly perplexing. In San Francisco, bikes are allowed on BART (Bay Area Rapid Transit), although some stations prohibit bikes during specified peak hours (and these hours are not necessarily consistent among stations). Additionally, bikes are never allowed on crowded cars, according to BARTs bike rules. Who makes the call on when a car is officially crowded? On the positive side, there are three BART Bike Stations, and the Fruitvale station in Oakland includes a full-service repair shop. Muni, or the San Francisco Municipal Railway, is one of the most diverse public transportation fleets in the world with streetcars, alternative fuel vehicle, buses and more. While Munis newer diesel buses and trolleys have front-loading bike racks, the streetcars, cable cars and light rail vehicles are not yet bicycle-friendly.In London, a folding bike seems to be the way to go if you need to take your bike on public transportation. Folded bikes are allowed on the Tube, on buses (at the drivers discretion), and on the London Overground. Non-folding bikes are permitted on the Tube and the Overground within designated sections and at designated times, and bikes are always welcome on any London boat service at any time. Interesting, Amsterdams public transport company, GVB, only has this to say about bicycle regulations: Bicycles can be carried on the sole condition that the Transport Company has granted explicit permission to do so. And that enlightening explanation is located in the Animals and bicycles section of GVBs company rules.There are so many cities with so many various options and rules around the world that the only conclusion that one can draw with regards to bicycles and public transportation is that you need to investigate the rules before attempting multi-mode commuting or traveling. In many instances, local advocacy organizations compile these resources online, and the transit operators very often have cycling guides posted online as well. Jumping onto a train or a bus can be an incredibly convenient way to cover longer distances that may not be feasible everyday on a bike as long as your commute route and schedule are aligned with the rules and regulations of your citys public transportation options.