I saw it once back in Brazil and I got fascinated with the concept of a folding bike. Marcelo Siqueira introduced me a bike you could fold and carry.
Here in the US I was waiting the snow and cold go away to go back biking. I’d like a bike that I would not keep on the garage and I could bring to work and commute sometimes. I got a Citizen Gotham2 20″, 7-Speed with alloy frame.
Unfolding steps:
The Citizen 20″ bike bag:
After using the bag to store the bike it also folds and can be kept in the steam or rack:
I’ve been using it for some months and it is really good. Now I want to put some more accessories to make it safer like a night flashlight.
Rules for Metro (DC)
The general rule for bikes in the DC’s metro is on  WMATA‘s “Cyclists on Metrorail” document:
Bicycles are permitted on Metrorail (limited to two bicycles per car) weekdays except 7-10 a.m. and 4-7 p.m. Bicycles are permitted all day Saturday and Sunday as well as most holidays (limited to four bicycles per car). Bicycles are not permitted on Metrorail on July 4th or other special events or holidays when large crowds use the system.
There is an exception for folding bikes from WMATA‘s “Bike ‘N Ride Policy“:
Folding bicycles and non-collapsible bicycles of all types that are folded or disassembled and enclosed in carrying bags, cases or boxes are deemed “luggage” items and are permitted inside railcars at all times. The carrying bags or cases must be made of a sturdy material such as canvas, nylon or leather-type materials.
Update in September 17th, 2012: WMATA has announced that a bag is no longer required.