“Roll on/roll off” train service for riders using the bicycle trails between Pittsburgh and Washington, D.C., is coming.

The question is exactly when.

The Allegheny Trail Alliance, a coalition of rails-to-trails support organizations, hopes service can begin as early as spring. Supporters want it to be available at all Amtrak stops along the passenger railroad’s Capitol Limited route between the two cities.

An Amtrak spokesman was not as confident about a 2011 start-up. “We are interested in doing this, but there are some basic operation issues that have to be settled,” said Steve Kulm, media relations director.

Existing Amtrak equipment has to be adapted for the safe storage of bicycles, he said. Decisions remain to be made on whether bikes would be carried in baggage cars or on racks in passenger cars. Train schedules likely would have to be amended to reflect the extra time needed to load and unload the bikes, he said.