Strengthened surveillance: The KCRC will install train- and track-based instruments to monitor wheel-rail interaction of East Rail trains.

Excessive vertical vibrations caused by uneven rail tracks and imperfect welding are the root cause of cracks found in the support brackets of East Rail train underframe equipment, the Kowloon-Canton Railway Corporation says.

The investigation report released today noted there are two main factors, the combination of which contributed to the occurrence of the cracks found on December 21.

The probe found the force of vertical vibrations was excessive when a train was travelling at 70-90kph over some sections of track. The excessive vibrations were due to the train wheel interacting with the minute undulations on the track surface. The stress levels encountered by the support brackets exceeded the original design limits by 100%.

Problem tracks

Test findings showed a strong correlation between the occurrence of the minute undulations and a batch of rail supplied in 1998-99 for a track renewal programme, which now makes up 36% of the East Rail line.

The second factor is attributed to imperfections in the welding of some of the underframe mounting brackets. The train manufacturer felt the mounting brackets were adequate, and the KCRC will seek independent advice.

For details of the investigation report click here. KCRC Chairman Michael Tien said the board has considered and accepted the report.

Passenger safety

"I have always remained confident that passenger safety was not at risk during and after the incident, and the investigation confirms this key finding in the report. The report also confirms that the KCRC staff involved in handling the December 21 incident and their subsequent actions, performed their duties with due diligence and in a professional and competent manner," Mr Tien said.

"The report also confirms that KCRC maintenance staff have been following closely the manufacturer's maintenance guidelines, and there is no evidence to show that lack of due diligence to the occurrence of cracks on their part is a contributory factor."

Noting it is not practicable to remove the minute undulations along the rail top due to the limitations of the existing maintenance equipment, the board has approved a series of improvements, like:

* reinforcing and upgrading all underframe equipment mounting brackets;

* enhancing the suspension systems of the entire fleet of all 348 mid-life refurbished train cars; and,

* replacing the critical sections of rail that have exacerbated the vertical vibrations.

These measures will enable mid-life refurbished train cars to withstand the measured level of vertical vibration. All of these works are targetted for completion next year.

Maintenance enhanced

While findings of the investigation and independent reviews by specialist consultants show KCRC maintenance standards and procedures have not been a contributory factor in the occurrence of cracks in the underframe equipment mounting brackets, maintenance procedures for the mid-life refurbished trains will be strengthened.

Moreover, train-based and track-based instruments will also be installed for continual surveillance of the wheel-rail interaction so further corrective actions, if needed, can be proactively implemented.