This week will not be remembered only for the arrival of the Beijing Olympics torch on Chinese soil. Sadly, the Hong Kong stage of the torch relay today will take place under the shadow of tragedy. The terrible Sai Kung bus crash is one of the worst traffic accidents our city has seen. There will be room in our thoughts today for the victims and their families and friends. Public transport lies at the heart of daily life in Hong Kong, be it a working day or, like yesterday, a holiday. Even if we are not one of the many who use it every day, most of us place our faith in buses or trains from time to time. The fact that the victims yesterday were mostly elderly people on their way to a religious gathering is a poignant reminder of that. Accidents like this immediately pose the question, how could this happen? Hopefully the police investigation will clearly establish the cause. An inquiry by an expert panel may also be needed, to recommend steps aimed at preventing similar tragedies. A precedent is to be found in the panel on highway safety appointed after the Tuen Mun bus disaster in 2003. In that case, 21 people died after a bus collided with a container truck and toppled 31 metres off an elevated section of the Tuen Mun highway. The panel's report found many other spots where similar accidents could occur and made wide-ranging safety recommendations. The stretch of highway approaching the roundabout where yesterday's accident occurred is downhill. While the police deny it is a black spot, the district council had expressed concerns about speeding. As a result, police have conducted anti-speeding operations. And roadworks have improved driving conditions, with two lanes instead of one. Road signage to reinforce driver-safety awareness includes advice to drivers of heavy vehicles to engage lower gears downhill. The operator of the seven-year-old bus says it passed safety checks less than a month ago. There is, therefore, no obvious reason to believe that this was a serious accident waiting to happen. The bus does not seem to have been overloaded, given that it was carrying the 62 occupants it was permitted to. There are, however, suggestions that speed was a factor in the accident. Police arrested the driver on suspicion of dangerous driving causing death. According to some reports, he claimed that the brakes had failed. The police investigation must clarify these issues. It may also find that a factor in the severity of the casualties was that the roof of the bus was crushed by the impact of the collision with an anti-noise barrier after it flipped on its side on the roundabout. This raises the question whether the planting of shrubbery or some other form of cushion to absorb impact in potential accident areas is a practical safety measure. The government is to be commended for its prompt response to this public-holiday tragedy. Chief Executive Donald Tsang Yam-kuen moved quickly to ensure that relevant departments responded to the needs of victims and families. A joint media briefing by police, social welfare and home affairs departments and the Hospital Authority ensured the public was kept fully informed. The priority now must be the thorough investigation promised by Mr Tsang to establish the cause of such terrible loss of life. That will, in time, help bring closure for the bereaved and injured. It will, hopefully, also identify measures which can help make our roads safer.