Since 2009, state transportation engineers have been working with civic leaders and residents in downtown Miami and Overtown to develop a long-promised, soaring “signature’’ bridge to replace the unsightly, obsolete Interstate 395 overpass, which has for decades cast an oppressive shadow over the area.

But even as a citizens’ committee picked a design for a dramatic suspension bridge dubbed the Wishbone Arch last month, Florida Department of Transportation consultants sprung what participants say was an unpleasant surprise: a less-expensive design for a plain-Jane “segmental box’’ bridge that the state also wants to consider.

FDOT District Secretary Gus Pego stresses that no decision has been made and that the agency has yet to identify funding to build any of the alternatives. Pego said he wants the public to think about the segmental box option because it would drop the price tag for the new highway by about $114 million, from the $673 million estimated cost of the version with the Wishbone bridge.

The last-minute introduction of the stripped-down concrete bridge, however, has provoked a flurry of unfavorable reviews from the Downtown Development Authority, Miami-Dade County officials and former Miami Mayor Manny Diaz. During his administration, Diaz won agreement from FDOT to erect a new super-elevated bridge that would undo some of the economic and aesthetic damage inflicted on Overtown and Biscayne Boulevard from the current span’s construction in the 1960s.

“A storm is brewing over this issue,’’ Miami-Dade Commissioner Dennis Moss warned during a recent meeting of the Metropolitan Planning Organization board after Pego, citing a conflict, canceled an appearance to explain what was going on. “That bridge has to be iconic. It has to have a ‘wow’ factor.’’

Added MPO vice chairwoman Maritza Gutierrez: “He [Pego] understands the gravity of the issue and he is prepared for the rainstorm. But I don’t know if he realizes it might be a hurricane.’’

The replacement of the I-395 span, which FDOT says is structurally and functionally deficient, has been seen as a critical piece in efforts to transform its once-depressed surroundings — which now include new condo towers, the Arsht Center and the arts and science museums under construction in nearby Bicentennial Park — into a cohesive arts, cultural and entertainment center. A distinctive bridge, supporters say, would become a symbol of the city’s resurgence.

Pego defended the vanilla-bridge scheme, calling it “a good-looking segmental bridge’’ similar to the nearby Port of Miami bridge that’s illuminated in purple light after dark. Unlike the Wishbone Arch, which would have no columns for most of its 600-foot length, the 300-foot-long segmental box version would be supported by piers.

“I want to build a signature bridge, don’t get me wrong,’’ Pego said in an interview. “But I want to make sure people realize what the difference in cost is. My thought process is, ‘Why is this being thrown off the table?’ What I’m trying to do is, let’s get the dialogue going on how we can afford the project.’’

The 1.2-mile I-395 span, which connects Interstate 95 to the MacArthur Causeway bridge along a series of elevated bridges and embankments, has been considered a source of blight virtually from its construction. It split the mostly black Overtown historic district, forced the relocation of thousands of residents, and established a physical and psychological barrier between downtown Miami and neighborhoods to its north. During the 1990s, areas under the I-395 overpasses in Overtown became homeless encampments.