What is the difference between 지나다 and 지나가다?
My dictionary lists both words (지나다 and 지나가다) as meaning "to pass by". Is there any difference between these words? If so, in what situations would the different words be used?

Question

Answer

비슷한 의미지만, 지나다는 주로 상태를, '지나가다', '지나오다'는 동작에 중점을 둡니다.

지나다. (상태를 주로 묘사함)
1. to pass or to go by (period of the time or some place) 
2. to exceed or to go beyond the limits. (비슷한 말, 지나치다)
3.

지나가다, 지나오다 (동작을 주로 묘사함)

지나다+가다.  pass and go. 
지나-아-가다 (연결어미 '아'가  붙지만, '아'가 모음탈락됨)
지나-가다

지나다+오다
지나오다. pass and come

Answer

The meaning is same, and they are interchangeable in most cases,
but sometimes one is more natural than the other depending on the context.