With a total length of 55 kilometres the mega bridge is the longest and most technically advanced in China. It is also the most expensive, estimated at US$17 billion, reported Hong Kong Economic Journal.

For the 6.7 kilometre underwater tunnel section, builders laid 33 sections of tunnel on the bed of the Pearl River, each weighing as much as an aircraft carrier.

During a public hearing in Zhuhai on December 21 organised by the Guangdong Development and Reform Commission (GDRC) officials said that they expect annual traffic flow of 21 million vehicle/journeys and annual income of CNY2.2 billion (US$338.29 million) over the first 30 years. They did not say when or if they would recover the investment cost.

Others at the hearing said that official projections of 65,000 vehicles a day using the bridge were too optimistic, given that there would be in future five bridges and tunnels that cross the Pearl River.

GDRC put forward two pricing plans. In both, private vehicles and taxis would pay CNY150 to cross the bridge, cargo trucks CNY115 and ordinary trucks CNY60. Coaches would pay CNY200 in one plan and CNY450 in the other.

Who will use the new bridge? On December 12 the HK Transport Department announced that it had agreed with the Guangdong government to increase the quota for HK cross-border private cars using the bridge from the 3,000 announced on August 25 to 10,000.

There is also a quota of 300 private cars in the mainland. Currently, 28,000 vehicles in Hong Kong and 3,000 in Guangdong have cross-border licences. They can also use the bridge.

Chief research officer at the Hong Kong-based One Country Two Systems Research Institute Fang Zhou said that delays in the construction of the bridge had given cities in the PRD time to greatly develop their port capacity, resulting in a situation where many exporters in the delta no longer need to use Hong Kong.

"Other PRD bridges will offer lower tariffs than the new bridge, while existing cargo barges to Hong Kong are even cheaper," he said. "In terms of time and convenience, the bridge is not so competitive."

The strongest economic argument for the bridge is traffic to Hong Kong International Airport (HKIA). In 2016, it handled 4.52 million tons of air cargo. Of this cargo, high value items that must be shipped quickly account for 10 per cent by volume but 40 per cent by value. The main items are fresh food, flowers, fashion, electronic goods and pharmaceuticals.

The bridge will enable producers west of the Pearl River to move their goods to HKIA more quickly.