Twelve rail cars already are on island for three of the 20 trains that will shuttle passengers along the city’s rapid transit line, and another was transported Tuesday morning to Waipahu from Honolulu Harbor.

There will be four rail cars to each train, and there are enough rail cars already for three trains in house at the Honolulu Authority for Rapid Transportation’s rail operation center.

Tuesday’s delivery is the first for a fourth train, and three others to complete the fourth will make their way to Waipahu from Honolulu Harbor on Thursday, Friday and Saturday, HART spokesman Russell Yama­noha said.

Each of the rail cars is about 60 feet long and costs about $2.2 million.

The first phase of the $8 billion-plus project, from East Kapolei to Aloha Stadium, is expected to begin in December 2020.

When the rail system is in full operation, 17 of the trains will be running during peak hours. There will be 21 stations along the 20-mile track.