While the state pursues a federal grant to study high-speed rail, local efforts are moving slowly to get commuter trains running between Charleston and Summerville.

The idea of putting passenger trains on existing freight rail lines between Charleston and Summerville, with possible service to other towns, may sound simple, but it's a costly venture that's been under study for years.

The bottom line today is not much different than it was years ago: It's still being studied.

A study completed in 2006 estimated that a commuter train serving Charleston, North Charleston and Summerville would attract more than 1,600 round-trip passengers daily.

A more detailed "phase two" study aimed at taking a closer look at the cost and benefits for passenger trains was launched the following year, and there's no firm date for when it will be finished.

Jeff Burns, transportation planner for the Berkeley-Charleston-Dorchester Council of Governments, said the study is nearly complete, and that it's been taking so long because the scope was expanded. Planners are looking into land-use plans that could change assumptions about ridership.

"The variable is the future land use," he said. "How are we going to match where people live with where they work and make our existing facilities work."

The success of passenger trains can depend upon the population density near train stations, as well as the cost and speed of rail travel when compared with automobiles.

Burns said the rail study also was delayed so that a related study on regional transportation could be completed first.

"We've extended the timeline, but it gives us a better product," he said.

The quality of the study could be important if federal funding eventually plays a role in local passenger rail service.

By most accounts, it could take a decade to create a commuter rail service, and costs could easily top $50 million.