It is a case of 'one country, two driving systems' for Hong Kong and the mainland - the subject of much debate both before and since the handover. While the mainland drives on the right, Hongkongers do so on the left as a legacy of the colonial past. Although there has been a sharp growth in cross-border traffic over the past 20 years, nothing has been done to unify the two systems. Over the years, there have been calls for Hong Kong to switch to the right, but that idea proved too radical a change for many and there has been strong resistance to the concept. Wong Chung-san, chairman of the Driving Instructors Association, stressed that drivers should be alert while driving across the border. 'Accidents are more likely when drivers are in an unfamiliar environment and cannot rely on their instincts,' he said. Andrew Windebank, the chief executive officer of the Automobile Association, said there should not be too many problems unless the number of mainland vehicles coming into Hong Kong increased dramatically.