The BART Go SDK by Rafael Espinoza allows developers to integrate the BART API into their Go applications. This SDK supports API functions for advisories, real-time estimates, routes, schedules, and stations and outputs JSON.
UK newspaper The Guardian is expanding its Open Platform (our Guardian API profile). The new API covers information about politicians and elections in the UK, with many details going back to 1992. It also contains limited older data, as far back as 1945.
As a DC-area resident, I've been one of many local developers saying that the DC Metro needs some sort of API. If anything, just to be able to build or integrate transit routes into existing apps. The wait appears over and the Washington Metropolitan Area Transit Authority now has an API.