A proposed two-towered, cable-stayed Francis Scott Key Bridge replacement would vertically dwarf the felled span and have slightly more space between its main piers, the first public rendering of what a new bridge could look like shows.

The preliminary design is included as part of an application the Maryland Transportation Authority submitted this month to the U.S. Coast Guard for navigational approval. The plans are conceptual, the application states, and a spokesperson for the authority, which owns the bridge, cautioned that the purpose of the document is simply to generate feedback from mariners and other interested parties.

Comments on the navigational clearances included with the rudimentary rendering are due to the Coast Guard by Dec. 7. Officials are working to design and rebuild the structure knocked down by the Dali container ship on March 26, with a goal of completing the nearly $2 billion project by fall 2028.

The 984-foot vessel lost power before striking a support pier and toppling the span. The disaster killed six construction workers and launched months of cleanup, what is expected to be years of litigation and government probes, and uncertainty regarding whether the federal government will fully fund a new bridge.

The authority’s application shows the original span, a truss bridge completed in 1977, overlaid by a cable-stayed sketch that could become a mainstay of the Baltimore skyline until the 2100s, and it puts pen to paper on two essential figures already determined by the Coast Guard: horizontal and vertical parameters that increasingly large ocean liners crossing under it must navigate.

The Coast Guard previously stated that the bridge must allow for at least 230 feet of air draft — that is, the space between the water below and the underside of the roadway — and at least 1,100 feet of horizontal clearance. The preliminary drawing depicts 230.9 feet of vertical clearance.

That would provide a roomy ceiling, substantially higher than the destroyed span’s 185 feet, and make it one of the taller bridges leading into any port in the country. The Bayonne Bridge spanning New Jersey and New York, for example, had its clearance raised from 151 feet to 215 in 2019 to allow for the growing size of cargo ships.

As a result of the increased clearance and the towering pylons necessary for a cable-stayed bridge, the new structure could rise nearly 200 feet above the old span — picture almost a Shot Tower’s worth of additional height — to make it between 500 and 550 feet tall.

The proposed Key Bridge’s minimum horizontal clearance, which includes the 800-foot-wide shipping channel, would be at least 1,100 feet, essentially the same as the old span.

Vertical clearance is important because it indicates how much space a ship has to fit under a bridge without colliding with the roadway. But horizontal clearance is essential from the perspective of risk mitigation. There isn’t a question of a cargo ship that is roughly 160 feet wide, like the Dali, fitting within a 1,100-foot gap. But if something goes awry, from inclement weather to a power outage, more space between the channel and the support piers offers a cushion of safety.

Twice in the span’s 47 years, a main pier of the Key Bridge was struck by a large vessel. The first time, in 1980, caused only some damage. The Dali’s strike this year plunged the span into the water in a matter of seconds.

The authority’s preliminary design notes the proposed bridge design would allow 1,100 feet between the “areas of proposed pier protection surrounding the main piers” and about 1,400 feet between the piers themselves, which could be a sufficient gap.

Anil Agrawal, a professor of engineering at the City College of New York, said the proposed main span’s length would be fine, and Captain Jeffrey Monroe, a master mariner who consults on bridge construction and renovation projects, said the span should be “more than adequate.”

The nation’s bridge code, however, warns against a main span that short.

Included within the code — a 1,904-page document with an equally hefty title: the “American Association of State Highway and Transportation Officials’ Load and Resistance Factor Design Bridge Design Specifications” — is a suggestion that a bridge’s main span should be at least double that of the channel length (800 feet, in this case) and two to three times that of the “design vessel length.” That means the Key Bridge’s main span should be at least 1,600 feet.

Bridges that don’t meet this criteria, the code states, are “particularly vulnerable to vessel collision.”

During an August talk sponsored by Florida International University, two of the nation’s foremost experts on bridge and vessel collision, engineers Michael Knott and Mike Winters, highlighted the importance of a lengthy main span.

“If the channel width were 1,000 feet, then the main span should exceed 2,000 feet, in this example,” Winters said during the August presentation.

There are many bridges in the U.S. that do not meet this guideline, but some newer bridges feature spans with plenty of length. The Gordie Howe International Bridge, which will connect Michigan to Canada, is expected to have a main span of 2,800 feet, which would make it the longest of its kind in North America when it opens, scheduled for next fall.

Many factors go into the possible length of a main span, from costs to construction timeline to the right of way on which a bridge owner has the ability to build. A lengthy main span can cause a project’s price to rise, Auburn University engineering professor Andrzej Nowak noted. The Gordie Howe Bridge is expected to cost more than $4.6 billion.

The transportation authority’s application to the Coast Guard outlines other dimensional differences, too, such as the fact that the new span will be wider to allow for larger shoulders on the roadway.

The plans call for the installation of six, 75-foot-in-diameter “dolphins,” which are protective, artificial islands, to fortify the approach span on the Dundalk side, along with to-be-determined pier protection around the remainder of the bridge. Those proposed dolphins would be significantly larger than the four that remain in the Patapsco River, a vestige of the fallen bridge, but would not be as strong a system as seen in some other modern bridges.

Asked for specifics on the pier protection system and the length of the main span, an authority spokesperson emphasized that the design is in its earliest stages and elements of it could change.

“While a bridge type is depicted for the purposes of illustrating impacts, it should not be interpreted that the final bridge configuration has been determined,” the spokesperson said in a statement.

A more robust system of dolphins or rock islands protecting the piers is among alterations that could be on the table, according to experts.

Before construction of the new structure begins, the Key Bridge’s remnants will be removed, down to 2 feet below the mudline. Demolition of the remaining structures, which will require blasting, diving and sawcutting, according to the contracted builder, Kiewit, is expected to begin early next year, the authority said.

President Joe Biden, who leaves office in January, promised the federal government would fully fund the rebuild of the Key Bridge (while seeking damages from the responsible party later) and recently included Key Bridge funding in a $100 billion disaster request to Congress. However, efforts to codify 100% federal funding into law have stalled all year. If Congress doesn’t take action, the federal government would pay 90% of the bridge cost, while Maryland would be on the hook for the remaining 10%, expected to be nearly $200 million.

“Our current financial plan assumed the 90 percent funding based on provisions for the Federal Emergency Relief program,” the transportation authority said in a statement, adding that, in that event, the cost would be covered with fees from Maryland toll facilities.