Mechanic Doug Mack keeps a trolley working in CARTA's fleet of buses at its maintenance facility on Leeds Avenue on Friday April 20, 2012. (Wade Spees/File)

Coming off a record year for ridership, the news that CARTA is several million dollars in debt is a serious threat to encouraging momentum for public transportation in the Lowcountry.

But rather than allowing a bus system clearly moving in the right direction to run off the road, Charleston area residents should rally to support it.

According to a Post and Courier report Wednesday, the Charleston Area Regional Transportation Authority owes about $6 million to TransDev, the company that operates the bus system. That debt should soon be covered by delayed federal funds, which provide the second largest portion of CARTA’s operating budget. Charleston County is the largest source of funding.

But CARTA also needs about $40 million over the next five years to replace critically aging buses, many of which are nearly 20 years old. The federal government has allocated money to replace a few vehicles, but CARTA can’t use those funds without a local match.

To that end, Charleston Mayor Joe Riley has included $470,000 in next year’s city budget, which could be used to replace some of the free trollies that CARTA operates on the peninsula. City Council should approve the request.

The need for community support for CARTA is made all the more imperative by the recent revelation that at least one national interest group has taken a keen interest in South Carolina’s public transit infrastructure. And they are not fans.

“We are opposed to spending gas tax money on public transit. A lot of folks don’t know that their tax money goes to certain projects,” said Dave Schwartz, the S.C. director of Americans for Prosperity, one of the primary advocacy groups financially backed by the Koch brothers.

Under the current state Department of Transportation long-term spending plan — which estimates a $40 billion funding shortfall through 2040 — a fraction of road money would support existing and new public transit, bike lanes and other non-car infrastructure. Gov. Nikki Haley has proposed raising the gas tax, in combination with an income-tax cut, to help DOT cover the shortfall.

Mr. Schwartz also asserted that his group considers such investments as bike lanes and commuter rail to be “silly” uses of public funds given that they don’t produce enough revenue to be self-sustaining.

He called the fact that CARTA recoups only a small percentage of its budget in fares “insane.”

That’s a profoundly wrongheaded approach. Public transportation systems are almost never self-sustaining. That doesn’t mean they aren’t valuable uses of public resources, or that they don’t provide tremendous public benefit.

For one thing, CARTA is an absolutely vital resource for the riders who took more than 5 million trips on it in 2014.

And with traffic congestion a top concern for thousands of Lowcountry residents, CARTA helped take 12,500 cars off the road every day last year. For comparison, that’s nearly 10 percent of the daily traffic on Interstate 26 between Charleston and Summerville.

That corridor is the focus of an ongoing Berkeley-Charleston-Dorchester Council of Governments study to investigate a new public transit alternative for the Lowcountry’s busiest route. The options currently on the table include light rail, commuter rail and bus rapid transit, among other possible choices.

In coming months, the COG will hold a series of public meetings to discuss the organization’s findings. A finalized transportation plan — including how to pay for its construction and operation — should be ready for submission to the Federal Transit Administration by December.

While a new transit alternative along I-26 could still be years down the road, CARTA is serving the community effectively every day. And more and more people are recognizing that fact by hopping on the bus.

Lowcountry leaders should embrace that overwhelmingly positive trend.

Give CARTA the assistance it needs to continue to connect local residents, take cars off the road, boost local businesses and make the Charleston area as welcoming and accessible as possible.