PORTLAND – Federal officials have given conditional approval to a plan to locate passenger rail track next to Interstate 295 through the city of Portland.

In a letter to the city, State Transportation Commissioner John Melrose said such approval would make it unnecessary to pursue other routes that have drawn opposition from residents and businesses in the Bayside neighborhood.

The Federal Highway Administration’s green light is conditional on the outcome of traffic forecasts for the I-295 off-ramps at Forest Avenue and the Franklin Arterial.

Alternate plans offered by the state would place tracks on either Kennebec and Somerset streets or along Marginal Way.

Amtrak service between Boston and Portland is expected to start later this year, with trains initially scheduled to stop at a station off outer Congress Street. The city hopes to build a permanent station off Marginal Way, which would require construction of new tracks.