> This causes a slight discrepancy in the bar graph, as the cost of living figures assume all parents to be working, but the income assumes only one working parent.

That seems like a pretty big discrepancy, and makes the cost-of-living vs pay comparison meaningless. If you assume each parent contributes equally to their cost of living, you would pretty much halve the 'cost-of-living' line on the chart.

Even if the other parent only makes 50% of what the bart employee parent makes, it would pretty easily close the gap between pay and COL for most of these positions.