Potential routes for passenger rail service between Phoenix and Tucson have been narrowed to three, said a news release posted Tuesday on the Arizona Department of Transportation website.

One route, known as the "green alternative," would parallel Interstate 10 between the two metro areas. A second, the "orange alternative," would service East Valley communities in Phoenix and run along the proposed north-south freeway corridor. The third, the "yellow alternative," would serve East Valley communities and share the right of way with Union Pacific tracks north of Eloy.

All three proposed routes would would parallel I-10 south of Eloy, the same as the current Union pacific tracks.

“The support for a passenger rail system that connects our state’s two largest metropolitan areas has been tremendous,” ADOT Director John Halikowski was quoted in the news release as saying. “It’s important to plan for multimodal travel options as we look ahead to the future of Arizona’s transportation infrastructure and as our state’s population continues to grow.

Next steps this year include public informational meetings in communities along the corridor, with the goal of identifying "one preferred alternative for further study by the end of 2013," the news release said.

Public hearings and a public comment period are planned for early in 2014, when an environmental impact study would be completed.

There has been little discussion so far of what the cost would be to build a passenger rail system between the two cities and where the money would come from.