For comparison, St. Louis always runs 2-car trains, since the tunnels on the oldest section of the line limited the system to 200' platforms. Yet with 40-some miles of LRT, and 2 overlapping lines, they now have 5-minute peak frequency where the lines overlap (10 minutes on branches), but could do 3.5-minute headways (7 minutes on branches), if not for cuts in state subsidies for operations. Similar to Charlotte, St. Louis has a fully gate-controlled, exclusive-ROW-running system operating at top speeds (no street-running segments like most other LRT systems). If St. Louis can handle 80,000 daily riders with 5-minute headways, I think Charlotte has a ways to go before added frequency would be so prohibitive that 3-car trains would absolutely be necessary.