One drawing envisions a sprawling Seurat-like park scene with the towers of Manhattan beckoning in the distance. Others call for two ghost piers beginning at opposite sides over the river but not meeting, elegantly terraced gardens and plantings, a simple walkway surrounded by wind generators, photovoltaic cells and other examples of green energy.

The idea of turning the existing Tappan Zee Bridge into a walkway and park when a new bridge is built remains more alluring dream than likely reality, though when Gov. Andrew M. Cuomo declared it in February to be an “exciting option,” that seemed to guarantee it would at least get serious scrutiny.

But since the proposal was floated last fall by Paul Feiner, supervisor of the Town of Greenburgh in Westchester County, enough people have become entranced by the idea that some have been imagining what it might look like, and have put those imaginings on paper.

Milagros Lecuona, an urban planning professor at Columbia University who with Mr. Feiner leads the Tappan Bridge Park Alliance, which is advocating the project, has worked with her class all semester on what it would take to make the park a reality. The New York Times also put the challenge to architecture students in Laila Seewang’s advanced urban theory class at Cooper Union. Ms. Lecuona is hoping to put together an international design competition to attract ideas for the Tappan Zee as park.