The El Paso City Council on Tuesday approved the map for the project that could cost up to $130 million.
Officials last month decided to spend $1.3 million for a preliminary study on building a trolley line to include the University of Texas at El Paso.
The El Paso Times reports establishment of a route allows city staff to continue studies and seek $90 million in state money.
Supporters say the trolley would promote economic development and increase transit ridership. Critics raised funding questions, with costs estimated between $20 million and $25 million per mile.
City Rep. Carl Robinson, who voted against the plan, says any rail project should cover the entire city.