As CARTA pursues its goal of replacing its fleet of buses, the question is not whether local governments should pitch in. The questions are how much — and for what.

CARTA’s new five-year strategic plan has a cost estimate of $40 million, 90 percent of which is eligible for federal and state funding, with $4 million in local matching funds required.

Still, the sticker shock is sure to inspire people to lament the cost of public transportation, and to question whether it is an appropriate expenditure of tax money.

While ridership has increased, people understandably complain when they see big buses with only a handful of riders.

Some see buses as being for others, and that providing transportation for them is too much of a financial drain.

The fact is that public transit systems rarely operate without significant government support. A city or county doesn’t get into the bus business because it sees potential for financial gain. Public transportation is an investment of a different kind. It is an investment in the community, the economy and the environment.

Without affordable public transportation, many low-income jobs would go begging because employees wouldn’t make enough to offset the additional costs of alternative transportation.

Some who use public transportation as a convenience would, without buses, crank up their cars, produce emissions, clog streets, use parking and put wear and tear on roads and bridges.

And those who do not live within walking distance of a grocery store might have to shop in an expensive and limited convenience store. Their children would have less healthy diets, and their family budgets would need further supplementing.

All that doesn’t mean, however, that CARTA shouldn’t aim to support itself financially as much as possible. And citizens certainly deserve reassurance that its board is considering all options — including light rail and electric buses.

The purchases CARTA makes today must be considered in the context of future regional growth and trends — both what people are inclined to do and what would be good for them to do to benefit the area.

Looking ahead five years isn’t enough. Try 20 or 25. Planning how to eliminate debt and get on stable financial footing isn’t enough if it doesn’t look beyond the status quo.

Would smaller buses suffice for some routes? When will light rail be feasible, and how does CARTA start planning now to achieve it? Has CARTA taken into consideration other work being done on transit like “Plans for Prosperity” for the Neck area of Charleston, the Council of Government’s “Our Region Our Place” report and the Peninsula Task Force’s recommendations for public transit?

Governments across the Lowcountry would make a costly mistake by failing to support public transit — or failing to insist that CARTA take the long view in its plans.