The bumpy rollout of the South Coast commuter rail service is the sort of debacle that fuels skepticism about transit investments. After $1.1 billion in public spending on the new routes to New Bedford and Fall River, how could the T and its contractor, Keolis, already be stumbling within a month?

More than a dozen trips on recent weekends have been replaced by buses because of what Keolis calls “crew availability” issues. Those buses have not always been reliable, as the Globe’s Shannon Larson reported last week, in some cases leaving travelers stranded for hours. “It’s very disappointing,” Fall River Mayor Paul Coogan told Larson.

Obviously, the most important thing now is for Keolis, a French company that has held the contract to manage day-to-day operations of the system since 2014, to get the trains running reliably. “They need to solve this problem,” said MBTA general manager Phil Eng.

Keolis said it had trained enough workers for the new service, including a buffer to cover employee sick days and vacations, but that the buffer proved to be not big enough on weekends, when there were more absences than anticipated. The company is now training more conductors and engineers. In an encouraging sign, all scheduled trains ran last weekend.

“We are truly sorry to the communities for what they’ve experienced these first few weeks,” a Keolis spokesperson told the Editorial Board. “We’re going to deliver the reliable service that folks deserve.”

Hopefully, riders who’ve been affected by the disruptions will give the service a second chance.

But just fixing the immediate problem isn’t enough; there also needs to be some accountability.

The T is crucial to Greater Boston’s economy. Getting more people to ride the train or bus instead of driving is also a major environmental priority. More and better train service can also cut highway congestion.

Outside the Boston bubble, though, funding for the T can be a tough sell. The fact that it already gets a penny out of the statewide sales tax — meaning that people in Pittsfield and Greenfield are funding trains they’ll never ride whenever they buy, say, a light bulb — is already cause for resentment.

More broadly, Americans are understandably dubious about the ability of government to accomplish anything and deliver services well. South Coast rail was already a symbol of skepticism in a different way — it took more than 30 years to complete.

Which is all to say that there’s a lot more at stake in whether South Coast rail runs well than just whether commuters in Fall River get to work on time, as important as that is. Effective, well-run services, and projects that are delivered in a timely fashion are the best counterarguments against critics who dismiss public investments as wasteful boondoggles.

The T has already fined Keolis $51,451 for service disruptions related to crew issues, and that’s a start. It would also be fair for the state to factor in the company’s performance on South Coast rail so far, and how well it responds to the interruptions going forward, into whether the firm is awarded the next contract to operate the system. (Keolis’s current contract is set to end in 2027.) If there were other factors that contributed to the disruptions that were beyond Keolis’s control, the T should identify them and make them public so they can be addressed.

For those who supported the South Coast rail project, including this Editorial Board, it’s frustrating to watch the service bumble out of the gate. Staffing problems can be solved, and there’s no reason to doubt that Keolis is sincerely trying to train enough workers. But, as the cliché goes, there’s only one chance to make a first impression — on commuters who might ride this service, and on taxpayers who might be called on to support the next one.

Editorials represent the views of the Boston Globe Editorial Board. Follow us @GlobeOpinion.