Driving across the border into China is jarring precisely because it is so seamless. One minute you are cruising along an orderly Hong Kong highway. Then, after a quick passage through immigration — a breeze compared to crossing the border on foot — you are plunged into the frenzied traffic of Shenzhen. It takes a moment to register the fact that you are now driving on the wrong side of the road.

Hong Kong drives on the left; mainland China drives on the right. It’s one of the most obvious differences between the former British colony and its estranged motherland, a reminder of how 156 years of colonial rule continue to exert a strong influence over every aspect of Hong Kong life. The Basic Law, adopted when China resumed control over Hong Kong in 1997, guarantees the city’s “way of life” will remain unchanged until 2047. But officials on both sides of the border are eager to tie Hong Kong ever closer to the mainland. You would be forgiven for wondering just how much longer the Special Administrative Region will keep driving on the left.

There’s a certain symbolism in a city that continues to operate as a mirror image of the country of which it is part. You could even read it as a measure of Hong Kong’s power and influence. When an elegant cable-stayed bridge was planned for Shenzhen Bay in the early 2000s, planners conceived it as a part of Hong Kong that extended into the mainland. And that’s exactly how the Hong Kong-Shenzhen Western Corridor has worked since it opened in 2007: traffic stays on the left until it reaches a border crossing located well into western Shenzhen. Hong Kong controls the mainland portion of the roadway and bridge, which it will lease from China until 2047.

The new 30-kilometre Hong Kong-Zhuhai-Macau bridge is just the opposite. As soon as vehicles pass through the border control facility located on an artificial island near the Hong Kong International Airport, they are on mainland territory, operated according to mainland rules – which includes driving on the right. That’s true despite the fact that only a small handful of mainland vehicles are allowed to drive on the bridge; nearly all of its traffic consists of vehicles registered in Hong Kong or Macau, which also drives on the left.

Traffic on the new link has fallen short of expectations since it opened in October, which has led some observers to speculate that it will be used as an excuse to allow more and more vehicles to cross the border. Currently, it takes a special permit to drive across the border, one that is held by about 25,000 Hong Kong vehicles and around 3,000 mainland cars. Urban issues watchdog Paul Zimmerman says former Chief Executive CY Leung is lobbying behind the scenes to allow all Hong Kong vehicles to drive in the mainland. “That in turn would start demands for reciprocal rights,” he says, raising the spectre that thousands more mainland cars could one day drive on Hong Kong’s roads.

That would quickly overwhelm Hong Kong’s limited road network, which already has the world’s second-highest density of vehicles per kilometre of road, after Monaco. But even if no more mainland cars are allowed into Hong Kong, Zimmerman says that allowing all Hong Kong drivers to drive in mainland China would have a similarly negative effect. At the moment, not many people in Hong Kong get around by car; on a typical weekday, 12 percent of people travel by private vehicle, compared to 32 percent in New York City. In a compact, congested city with excellent public transportation, most people just don’t see the use in owning a car. “However, if that vehicle can be used to traipse around the [Pearl River Delta], more people will be compelled to own one,” says Zimmerman.

That in turn could lead to a snowball effect: the more cross-border traffic there is, the more pressure there will be to harmonise driving standards between Hong Kong and the mainland. Transport expert Hung Wing-tat, who recently retired from teaching at Polytechnic University, says it is entirely plausible that Hong Kong could one day switch to driving on the right. “It is to the benefit of Hong Kong people to have the same side driving side [as mainland China] especially when it is mainly Hong Kong vehicles that are permitted to drive across the boundary,” he says. “It is safer for Hong Kong drivers.” It would even make buying a car easier, since most of them are manufactured for the Chinese, European and American markets – all of which drive on the right.

It’s worth stepping back to see how we got here in the first place. When the first automobile hit Hong Kong’s streets in 1903, it drove on the left side of the road, not only because Hong Kong was a British colony, but because that had been the accepted order of things for thousands of years. Archaeologists have determined that ancient Romans, Egyptians and Greeks kept to the left side of the road when they travelled. That began to change in the late 18th century when the United States and France, driven by revolutionary fervour, both switched to right-hand traffic as a way break away from the old order of things.

As France conquered large parts of Europe under Napoleon, it gradually made right-hand traffic the continental norm, which in turn spread to European colonies around the world. The US took up the torch as its own influence grew in the 20th century. In 1946, the American-backed Nationalist government in Chongqing ordered China to switch from left to right. Hong Kong may have followed suit if the Communists had not won the Chinese Civil War and sealed the mainland border in 1949. Cut off from trade with the mainland, Hong Kong relied on buses, cars and lorries imported from the UK. Macau kept driving on the left because of its close ties with Hong Kong, even though Portugal and all of its other colonies had switched to driving on the right in 1928.

Cross-border traffic wasn’t an issue until China’s economic reforms invited a flood of Hong Kong investment. As factories moved their operations to the mainland and Chinese-made products began to appear on Hong Kong’s shop shelves, the number of border crossings tripled, from two to six, with a seventh opening later this year. More than 675,600 people cross the border every day, and a growing number of them are cross-border commuters who work in Hong Kong but live in Shenzhen.

If the goal is further integration with the mainland, switching from left to right certainly makes sense. Hung says it wouldn’t even be as much of a hassle as it may seem. “The costs would be incurred largely to cover the changes in road infrastructure, [such as] junction turnings, road signs, road markings and traffic signal controls,” he says. Although he doesn’t have an estimate of how much it would cost, he doesn’t think it would be a “huge amount” of money. Zimmerman disagrees. “My expectation is that feasibility studies will show that it is too expensive, and too inefficient,” he says.

Whatever the financial cost, the symbolism is another thing entirely. Doing away with left-hand traffic would be an unmistakable break with the past – a leap towards a future as Xianggang, not Hong Kong. “The hurdle is not technical,” says Hung. “Rather it is the feeling of Hong Kong people. Over half of the population do not want to see changes to align with mainland in many social and political aspects.” In the current political climate, switching from left to right would be like sailing into a typhoon. That’s not to say it will never happen. But for now, just make sure to look both ways when you cross the street.