$1.4k is below average (but possible) in DC. I don't know anyone in SF who is paying $2.7k a month for a place (the high end condos go for that, but they're generally split by couples). The vast majority of people I know in SF pay under $1.4k a month for rent.
The rent is higher in SF, but the tradeoff is that you can walk or ride a bike everywhere, year round. It's possible to get by in SF without a car at all. In DC (or elsewhere) you're paying for parking, gas, insurance, and a monthly car payment. That starts to add up pretty quickly. There's not an $11k a year difference without that ($1.4k vs $2.7k isn't realistic), but factoring it in, SF really closes that gap, or likely becomes cheaper.
I think the tricky part is that there really aren't many apartment buildings in DC to begin with, aside from the recently built and very overpriced luxury condo conversions, so the supply of one bedroom apartments is low. If you can stand to have roommates, you're much better off with a 2 bedroom English basement or a 3-4 bedroom little rowhouse.