The Fouad Boutros highway overpass is a long-stalled project, dating back to before the 1975-1990 civil war, and intended to route unnecessary traffic away from some of the city's most congested areas.
For now, the only part of the route completed is a single bridge, which was finished before the war began and has remained as a lone reminder of the old plans.
The Council for Development and Reconstruction, a government organisation intended to help rebuild post-war Lebanon, says the road will significantly improve traffic in the city.
But it would run through some of Beirut's best-preserved old neighborhoods, home to traditional houses that have disappeared elsewhere in the city thanks to a combination of neglect and rampant development.
The road "will puncture the continuous street facade... destroy two beautiful buildings and run a few inches away from a palace," says a study commissioned by an NGO, Save Beirut Heritage (SBH).
"The perspective of the street will be blocked and disfigured by the huge concrete mass of the overpass: a visual nightmare."
The group argues that the project is the product of an outdated school of urban planning, pointing out an alternative way to alleviate traffic would be to upgrade Beirut's virtually non-existent public transportation system.
Moreover, the group says no impact study has been conducted on construction of the road.
The Council for Development and Reconstruction, in an emailed statement to Agence France Presse, declined to comment on the heritage impact of the road.
But it said the project would "alleviate the traffic congestion" in the area and denied that the plan had been unaltered since it was originally proposed.
"The link was redesigned in order to better suit local conditions and to answer to the development that occurred since the earlier design," the statement said.
The council said work would begin within months and is expected to last around two and a half years, with total costs approaching $60 million.
The tussle over the road is part of an ongoing battle between developers eager to upgrade the city's infrastructure and take advantage of demand for housing, and activists and residents desperate to preserve part of its history.
Beirut was once dotted with traditional Lebanese houses featuring triple-arched windows, elaborate balconies and red-tiled roofs. Facades featured elaborate engraving and unusual brickwork, each home a little different from the other.
The civil war left many of those homes damaged, and others abandoned, but development has since claimed hundreds more.
Of 1,200 old mansions and buildings inventoried in 1995 by the culture ministry, a mere 400 are left, officials said in 2010.
In place of the highway in the Mar Mikhail-Gemmayze area of east Beirut, SBH wants a smaller road project supplemented by a new park system to increase the city's green spaces.
"Wouldn't this money be better spent bringing Beirut's urban planning into the 21st century by creating green public spaces, optimizing existing road networks and creating long-term solutions with public transport?" it asked.