The MTR Corporation will give the tracks on its new lines a slight bowl shape to bend the train down when it leaves a station and raise it when approaching the next one, as a way to cut electricity consumption and reduce carbon emissions.
The new design is one of several eco-friendly measures the rail operator is adopting on its new lines.
All together, they should save the MTR Corp about 19,800 megawatt hours of electricity a year - equal to the annual consumption of about 55,000 households, its chief electrical and mechanical engineer, Leung Chi-lap, said last week.
By adopting a slight curve in the tracks, a train "can start with more energy and arrive with less", Leung said.
Passengers are not likely to notice the change as the gradient will be small.
The new design will be adopted on all five projects now in the works - the South Island line (east), Kwun Tong line extension, Sha Tin to Central link, express link from West Kowloon to Guangzhou, and West Island line. The projects are variously scheduled to finish between 2014 and 2020.
The MTR Corp estimates the lower energy consumption will reduce carbon dioxide emissions by 14,000 tonnes.
Another energy-saving measure is a "variable-frequency drive" that will be installed in new lifts and escalators. The feature harnesses the energy generated when the lift or stairs descends, funneling it back into the power supply for lighting, air conditioning and operation of screen doors on the platform.
Leung predicted the package of measures would require about HK$360 million in investment, but the MTR Corp did not aim to recover the expenditure.
In its latest annual report, the MTR Corp said the cost of energy and utilities, which included water, rose to HK$561 million in the first six months of the year up from HK$513 million over the same period last year.