The key to an efficient public transit system is the easy transference of passengers from one form of transportation to another. That's why ending the SMART rail line as close as possible to the Larkspur ferry terminal in Marin County makes sense. That's also why ending the SMART rail line — or at least the first phase of it — at the Guerneville Road station in Santa Rosa to the north doesn't.

Short of a few local bus lines, there is no other means of transportation at the site.

Common sense suggests a better terminus — short of extending the rail to Windsor, Cloverdale and other cities that were promised rail stations — is a stop at Airport Boulevard. Fortunately, common sense seems to be making headway.

Sonoma-Marin Area Rail Transit officials on Wednesday approved spending $6.6 million to buy an additional two-car train that will allow them to expand the frequency of service once the train is running, either in late 2015 or early 2016. Trains will now be able to run in 30-minute intervals.

The purchase also allows SMART to consider extending service farther north to Airport Boulevard.

In April, the SMART board agreed to buy 6.6 acres of land near Airport Boulevard and the tracks from the Sonoma County Water Agency for $2.7 million to build an operations and maintenance facility.

Construction on the facility is already under way, but SMART still needs to find funds to rebuild the track to that point.

Creating a station there makes sense. It would provide service to an estimated 6,000 workers in the business parks near the airport while also bringing passengers just a short shuttle trip away from the Charles M. Schulz-Sonoma County Airport.

Not to be overlooked is that over the next two years, the airport will be undergoing a $54 million expansion that will include extending the runway to allow more flights. Eventually, it will have a new passenger terminal, new control tower and more cargo space. Alaska Airlines, which operates five flights a day out of the airport, eventually could have up to 21flights a day. Having a quick shuttle connection to SMART would provide a critical service to passengers while helping minimize traffic impacts of the airport expansion.

State Sen. Noreen Evans, D-Santa Rosa, is trying to help by encouraging the Metropolitan Transportation Commission to allocate $15 million — a modest amount compared to the funding provided elsewhere — toward rebuilding the tracks to the airport site. As reported last week, MTC is expected to act on the request next month.

We encourage the commission to support the plan and provide the necessary funding to take SMART to the airport.

It's not the ultimate terminus that the public was promised, but it would be 4.5 miles closer. And it makes sense.