"Imagine something big," says John Cryer, an architect at Page Southerland Page. "Really big."

He's talking about the Pierce Elevated Freeway, the raised stretch of I-45 that hooks around the west side of downtown Houston. With an eye toward improving traffic flow, the Texas Department of Transportation is proposing to re-route I-45 — and to do so in such a way that would leave the roughly two miles of the Pierce Elevated out of a job.

And that, say Cryer and other urban dreamers, could be a huge opportunity for Houston. What if, instead of tearing down the Pierce Elevated at an enormous cost, the freeway structure became the base for an elevated linear park — a Houston version of New York's High Line or Paris's Promenade Plantée?

"Pierce Skypark," Cryer and two other Page architects call the idea. He, Tami Merrick and Marcus Martínez have been working on it pro bono, hoping that a powerful public or private entity would take the idea and run with it. Their presentations have been received warmly: Pierce SkyPark's Facebook page has more than a thousand "likes."

Martínez's dream-big conceptual sketches give a sense of the proposal's size and potential. The park that he and the rest of his team imagine would be 1.97 miles long, and cover 37.7 acres — an astonishing swath of parkland so near downtown. By comparison, New York's High Line, built atop an unused freight-rail line, is significantly shorter (only 1.45 miles) and much, much skinnier (13 acres).

What you can do The Texas Department of Transportation is accepting online comments through May 14.

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Besides the obvious paths for bikes and pedestrians, Martínez says, there'd be room atop the Pierce Elevated to install all sorts of attractions. Maybe a golf range; or a bike-in theater; a conference center; gardens; or a greenhouse for native plants to be installed along Buffalo Bayou.

Oscar Slotboom, the author of the book Houston Freeways, offers a different vision and different drawings. He emphasizes that a park focused on recreation — chiefly walking, jogging and biking — could be created at a relatively low cost. And he also notes the historic value of saving the freeway structure. Freeways, he notes, have shaped the Houston we know.

But essentially, both Slotboom and the Page architects make the same argument: That the Pierce Elevated should not be demolished. That tearing it down would cost the Department of Transportation millions of dollars. And that leaving it would give Houston the opportunity to create something great.

The Texas Department of Transportation is currently holding meetings and accepting online comments on its proposal to reroute I-45. (Downtown construction of the new freeway could start after 2017.) So the time for citizens to speak up is now, says Tami Merrick of the Skypark team.

"We wouldn't have to build it all at once," says Martínez. "We could build it in stages, as there's money, like they did with the High Line."

"And as long as we don't demolish the Pierce Elevated, we're in business," says Cryer. "It wouldn't take much at all to make it ready for bikes and pedestrians."

"The park could be a huge asset," says Slotboom. "It would be a shame to waste it."

Lisa Gray (@LisaGray_HouTX) runs Gray Matters.

Bookmark Gray Matters. By comparison, New York's High Line is significantly shorter and much, much skinnier.