The best thing the DC region could do to increase the amount of transportational (and possibly recreational) cycling is to continue expanding Capital Bikeshare (CaBi). In Paris, the introduction of Velib led to an almost instantaneous doubling of cyclists within the city. A study of world bike sharing programs shows that only about 5-10% of bike sharing trips would have been made by bicycle without bike sharing, so with 1000-2000 CaBi trips per day (depending on the weather) that's hundreds of thousands of new trips per year by bicycle already.
Since the transition from SmartBike to CaBi started, the system usage has already doubled from 1 trip per bike per day (tbd) to 2 tbd. Montreal was getting about 2.2 tbd after opening and Paris and Lyon are up closer to 7 tbd. Clearly adding stations has increased demand. While it may not be that DC has the population density to get to 7 tbd, it's not clear that we've peaked at 2 tbd. In fact adding more stations, as both DC and Arlington plan to do as early as May, should still bring not only additional trips but increased tbd.
It's unfortunate that the region didn't win the TIGER II grant it sought this year that would have added ~2600 bikes to the system and expanded it into Montgomery County, Alexandria, Reston and College Park, but this expansion should continue as money becomes available. And there is room to expand beyond that as well. In fact I can think of several levels of saturation for the system that could be pursued as a reasonable goal.
The region could continue to adds stations until they reach a maximum tbd. At this point adding an additional station might add new members and increase the total number of trips but, because the only choices are to increase redundancy or move into low use areas, it would begin to drop the average tbd. That system would only serve the densest areas though, and so isn't a good goal.
The region could add stations until they reach a maximum number of members per bike. It may be this point has already been passed. CaBi has about 5 members per bike, but SmartBike had 16 members per bike. I'm confident that CaBi membership will continue to grow in the spring but we'll see if it gets as high as 16 members per bike. If it does, they could keep adding stations until they maximize membership per cost, but again, that involves serving only the densest areas.
Another inflection point they could aim for is maximum income - including possible carbon credits. That's what a business would do. Under such a scenario they would keep adding bikes and stations until the cost of an additional bike is less than the revenue it would add. But Capital Bikeshare is not a for-profit business - even thought there is a private business element to it. Each CaBi trip has some value to the region; because it gets someone out of a car, gets them to take a trip they would not have otherwise or saves the user time and/or money. A better goal than maximizing income is to maximize value. In this case, the value of each trip taken would be added to the income earned. So if each trip has a value to the DC region of $0.50 and the new bike would add 1000 trips per year, then they'd include another $500 in their calculation as to whether another bike would add value. It might even be that at maximum value, the system is losing money. This is the point at which they've reached market saturation - and where they should consider whether or not they've maxed it out.
If they wanted to reach true saturation though, they'd go for maximum trips. There is some point at which adding new stations will not add trips. Everyone who wants to ride a CaBi for a trip can and the lack of a docking station in some location or bikes at that docking station is no longer an impediment to using the system. That would probably be far too costly a goal - and a poor use of public money. Adding a docking station that will be used once a year doesn't make a lot of sense.
Regardless, they're a long way from having to worry about saturation, so more stations and more bikes should be the goal.
Photo by pablo.raw (BTW, not to be a grinch, but putting two people on a bike is illegal in DC)