While creative solutions were put forward about how to handle the side swap, including a "flipper bridge" called the Pearl River Necklace proposed by a team of Dutch architects, a less exciting approach was chosen in the end, with cars stopping and changing sides at a specially built merge point before they drive onto the bridge in Hong Kong.
China's President Xi Jinping officially opened the world's longest sea bridge connecting Hong Kong, Macau and mainland China Tuesday, at a time when Beijing is tightening its grip on its semi-autonomous territories.
"The bridge is not just a mega transport infrastructure jointly built by Guangdong, Hong Kong and Macau", Hong Kong's secretary for transport and housing, Frank Chan Fan, said on Friday.
Construction on the project began in 2009 but has been marred by delays and safety concerns.
In Hong Kong and Macau, drivers travel on the left, in mainland China, drivers travel on the right, presenting a bit of a conundrum for the bridge.
The bridge will open to regular traffic on Wednesday.
To allow ships through, a 6.7km section in the middle dips into an undersea tunnel that runs between two artificial islands.
Some critics, however, see the bridge as a white elephant that is part of a multi-pronged push by China to exert greater control over Hong Kong, which returned from British to Chinese rule in 1997 amid promises to preserve the city's high degree of autonomy and individual freedoms denied in mainland China.
"The collaboration between Guangdong, Hong Kong and Macao in terms of trade, finance, logistics and tourism will be strengthened".
Some Hong Kong media have dubbed Xi's trip, his second to Guangdong since taking office in 2012, as a "southern tour", echoing a high-profile 1992 visit to the special economic zones of the south by former paramount leader Deng Xiaoping. The construction of the bridge has dragged on for almost a decade - authorities started building in 2009 - and it has been plagued by problems, including suspicions that parts of the bridge were floating away.
Nine workers have died and more than 200 others have been injured building the bridge. Instead, a majority of traffic will come from shuttle buses or "special hire cars".
A Hong Kong government video explaining the ease of bridge travel, but which detailed a process requiring permits from Macau, Hong Kong and China, has been particularly mocked online. The bridge is not served by public transport.