18% of households in the DC area have at least one person who rides a bike for transportation "in a typical week." That, according to data released by the Census Bureau as part of the March 31 release of the 2013 American Housing Survey (not to be confused with the ACS), can be viewed as a floor, not a ceiling. There is likely a long tail of households wherein a member bikes "to any place inside or outside [their] neighborhood" less often than a "typical week."
2.5% of households responded that they biked in a typical week, 33.7% said they walked and 15.7% said they did both. All totaled 51.9% or Metropolitan households reported walking or biking in a typical week.
The survey data is a little clunky because it is done by household instead of person, and it reports for the whole DC Metropolitan area instead of by jurisdictions. The questions about biking and walking appear to be new so there's nothing prior to compare them to. You can see the survey here and the questionnaire here.
Reasons for not biking/walking
Unfortunately, they grouped biking and walking together when asking people the reason why they didn't bike or walk. Far and away the largest reason was the helpful "no reason" (must've been filled out by teenagers playing video games.) 79% of respondents listed that. But for those who did have a reason, health reasons, long distances and no sidewalks (remember it combined both modes) topped the list. DCInno has some good graphics showing this, but the article sometimes forgets that it's a question about biking and walking, not just biking.
Bike lane access
DCinno also has a graphic showing that the DC Metro ranks 11th among the 25 metro areas studied in bike lane access. Tucson, surprisingly, is #1.
Access to places
Included were a series of questions about what kinds of places one could access by foot or bike from their homes.
The responses to these are questionable, probably due to ignorance by the public about biking and about how to get around their neighborhood without a car, don't always make sense. The most glaring example of this is that, across the board, more people claimed that a place was accessible by walking, but not biking, then the inverse. For example, 2.5% of household can reach a grocery store by bike only and 9.7% claim they can reach one by foot only. There may be places that one can access on foot, but not on bike, but they are surely dwarfed in number by the places one can access on bike but not on foot.
The percentage of people claiming they can reach a place by bike are shown below:
Breaking the data down by subgroups, homeowner households (19.2%) bike more than renters (16.2%); people in new homes (13.6%) bike less than average, but those in mobile homes (23.4%) bike more; all-black households(10.6%) bike much less and all-hispanic households bike more (23.7%); unsurprisingly, the elederly (5.6%) don't bike much, but surprisingly neither do those below the poverty level (9.9%).
For walking (average all households = 46.6%), homeowner households (46.6%) walk less than renters (54.4%); people in new homes (44.6%) walk less than average, as do those in mobile homes (48.3%); all-black households(40.6%) walk much less and all-hispanic households walk more (58.5%); the elederly (38.6%) walk less, and so do those below the poverty level (45.5%). But the deviation for the subgroups for walking is less than for biking.
16% of area households have bike lanes nearby and 74% have sidewalks. 14% of sidewalks are identified as inadequately lit.
The monthly transportation costs question, unfortunately doesn't include bike expenses, just cars and public transportation. The average median monthly transportation cost for driving is $875 a month and for transit is $40 a month (but that is for all households, not just those that use transit or cars).