It is like He had a trip to Beijing. 他去了北京= He went to Benjing 他去了北京一趟=He had a trip to Beijing. and we use it pretty often I think :)

趟是个量词，表示来往（走动）的次数。it is a measure word，means one round trip. Its radical is 走，so originally it is related to walk. For example : 你走一趟吧。

it means one time！

normally 一趟 means 一次（once，one time）. it normally used when the person isn't there at this moment .it always used to emphasis "go somewhere and back from(or leave) there". you can say 去了两趟，means“ went there-->back/leave from there-->went there again-->back/leave from there again" it is always used in Mandarin and mostly in Beijing language.

趟 = classifier for times, round trips or rows / a time / a trip