Alexandria is seeking to transfer a $1 million grant for road work to take the next steps in determining where to build a Metro station at the Potomac Yard shopping center.

The city is seeking the money though the Northern Virginia Transportation Commission to help study three alternatives for where to build a station serving the Yellow and Blue lines. The grant helps cover part of the $4.3 million needed for an environmental evaluation, public hearings and preliminary engineering sketches.

The city already has some of the money needed for the study but wants to convert a Federal Highway Administration grant into an $800,000 Federal Transit Administration grant with a $200,000 state and local match, according to Richard Baier, director of the city's Department of Transportation and Environmental Services.

The challenge for the new in-fill station is that a set of CSX freight tracks lies between the Metro tracks and the Potomac Yard development. That means Metro train tracks would have to cross over the freight tracks or riders would need to do so on foot.

The city has two scenarios in which the station is built on the far side of the CSX tracks, connecting riders to the shopping area through two pedestrian bridges. One site is slightly farther north than the other.

A third option would entail building aerial tracks over the CSX tracks to an elevated station on the side of the shopping center.

The city is working on refined cost estimates, but initial estimates for the ground stations put the project cost at $497 million, with an estimated $74 million coming from developers and $194 million coming from a special taxing district around the area. The remaining $229 million could be covered by taxes gleaned from higher property values and other taxes spurred by the development, according to a city presentation on the plan.

The city is expecting to host public hearings on the plan in early-to-mid-2013. It hopes to have a final decision in early 2014. The earliest the station would open would be late 2016.