ROCHESTER — They were constructed in South Korea, spent more than a month voyaging across oceans to the United States and will eventually transport riders on the much-anticipated South Coast Rail, which extends service to New Bedford and Fall River.

But for now, these shiny, spotless new Massachusetts Bay Transit Authority cars sit on indoor tracks in an unlikely location: Rochester. 

To be specific, they are being held and inspected at the Rochester Maintenance Facility, where some MBTA equipment is repaired.

“It’s the best-kept secret of the MBTA,” said Bill Wolfgang, director of vehicle engineering for the MBTA, of the Rochester location, which straddles the town line with West Wareham down a long road in a secluded, semi-wooded area.

The four trains that arrived June 10 in Rochester are the first of 16 new trains that will be used for the rail extension, said Salvatore “Joe” Trapasso, deputy director of commuter rail for the MBTA.

Their journey began in South Korea, where employees at Hyundai-Rotem constructed the cars to the MBTA’s specifications.

The completed vehicles were placed on a carrier ship on April 8 in the port of Masan, South Korea. The ship features a large door and folding ramp, so the cars could be rolled on and rolled off, Trapasso said.

The cars were located below deck, Trapasso stressed, where they were not exposed to the elements.

The ship arrived in the port of Baltimore on May 18. After being unloaded from the ship, the coaches were eventually delivered first to Middleboro by rail-based freight carrier CSX on June 10 and then to Rochester via Mass Coastal Railroad later that day.

These new vehicles differ from most current trains in several ways, Trapasso said. 

The new trains have two levels to accommodate more riders, Trapasso said. 

While most trains can fit 120 people, the added seating allows for 180 riders, which means that two trains can carry the same amount of passengers as three single-level ones.

Another more subtle change is the placement of electrical and charging outlets at the seated level, rather than low to the ground, to make electronics use more convenient for riders, he said. 

Twelve more trains in groups of four will be arriving before the end of the year. 

The exact date when the trains will take to the South Coast Rail tracks permanently remains unknown, Wolfgang said.

For now, the route taking the vehicles from South Korea, with related logistics and communication, takes up much of their focus.

That part of the project is ahead of schedule, he said, and is “looking good.’’