Ive been using this one for a few weeks now on an iPhone 5s. The times are really accurate, usually spot on to the normal DC Metro website AND the times listed on the Station boards. Once in a while, this app is a minute off. Literally one minute off, and that is only about 10% of the time. I have been comparing times for the last two weeks, and this app is really accurate. If you are the kind of person that cannot live knowing this app may be ONE minute off, then you need to re-evaluate your usage of the DC Metro system. Here is a solution for you - get to the Metro two minutes early.
DcMetroUser about NextTrain DC Metro - AR