The existing bridge, spanning the Hudson River between Westchester and Rockland counties in New York City's suburbs, is overcrowded and deteriorating after 56 years of use.
The planning document, from the Federal Highway Administration and state Department of Transportation, foresees the new bridge opening by 2017.
The 49-page "Scoping Information Packet" was posted online in advance of public presentations scheduled for this week.
The long-discussed replacement for the aging Tappan Zee was pushed forward earlier this month when President Barack Obama declared it eligible for fast-tracked federal approvals.
However, the anticipated mass transit aspects of the new bridge had been dropped, thereby trimming the cost to $5.2 billion, down from as much as $21 billion.
The Federal Highway Administration said at the time that transit components were "currently not a part of the design." Many New York officials, including Westchester County Executive Rob Astorino, called that short-sighted.
"I am troubled by the proposed design's absence of a mass transit component that would help alleviate congestion," Astorino said Tuesday. "A new bridge - without a mass transit component - would already be at capacity on the day of its opening."
The county executive suggested that bus rapid transit - which would mean bridge lanes dedicated to buses - could be included at a reasonable cost.
The new document emphasizes talks only of future mass transit.
It says one of the goals of a new bridge would be "providing a crossing that does not preclude future trans-Hudson transit services."
The plan calls for two separate four-lane spans - one eastbound, one westbound - to be built just north of the current bridge, and connecting to the riverbanks at the same locations.
The spans would be separated by a 42-foot gap. The document says that gap could be used in the future "to provide the infrastructure for future transit modes."
Builders will also consider the possibility of building two levels on each span. In previous studies, it's been proposed that a lower level be used for trains or other mass transit.
Unlike the current seven-lane bridge, the new bridge would have wide shoulders and include a bicycle and pedestrian path.
Even at the new, lower cost, funding is not yet in place, although the highway administration said earlier that the state plans to use toll revenues, labor pension funds, federal loans and other sources.
The document says the alternative of keeping the current bridge rather than building a new one will continue to be studied "as a baseline to evaluate the benefits and potential impacts" of a replacement bridge. The "no-build" alternative will be included in the project's environmental impact statement, the document says.
The document says it would cost $1.3 billion over the next 10 years to keep the current bridge in good repair. But it notes that the Tappan Zee "falls short of current engineering standards relative to seismic and security criteria."