Since I used the metro for impromptu movement rather than to make appointments, the biggest feature is high frequency. At peak times trains are every three minu

Since I used the metro for impromptu movement rather than to make appointments, the biggest feature is high frequency. At peak times trains are every three minutes in the DC metro, and the slowest seemed to be six minutes. 10 or 15 minute intervals, or the 20+ minute BART intervals, make a system very inconvenient.