The obvious variable is overhead per passenger mile - capital costs are pretty constant. For rail, costs per passenger falls as volumes rise.

The capital costs aren't shown - how would they compare to operating costs?

Variable costs also tend to fall as volume increases. 8 car trains take no more labor (one operator) than 6 car trains (OTOH cleaning crews are per car). Fully loaded cars use only slightly more electricity than nearly empty cars.

TOD takes time. Part of New Orleans success with streetcars (80+% to 100+% farebox recovery, is how well housing and living patterns are woven into the system (operating since 1834). The largest building in the city, 51 story One Shell Square, is in between the tracks of the St. Charles streetcar. After 5 PM it is hard to get a seat after the streetcar passes One Shell.

In addition, ridership increases on existing lines when a new line is opened. So the bigger the system, the more economic it is. Two lines are better than one line, Seven lines are better than six lines.

Best Hopes,

Alan

Best Hopes for Large, Dense Urban Rail systems,

Alan

Thanks!