Bangkok - To reduce carbon dioxide emissions - blamed for global warming - Asian cities of the future should grow vertically instead of horizontally, a leading transport expert said Wednesday.

"In many Asian cities, people are building new housing developments 20, 30, 40 or 60 kilometres out of town and this means people are taking longer to get to work," said Charles Melhuish, technical director with the UK government's Transport Knowledge Partnership.

"Instead, they should be developing a compact, high-rise city, which is also easier to serve in terms of power, water and sanitation. Each time you extend a city in a linear fashion, all the infrastructure costs increase fantastically," said Melhuish, a speaker at the Better Air Quality (BAQ) 2008 workshop in Bangkok, which has drawn about 900 participants.

Melhuish cited Singapore and Bogota, Colombia, as two cities that had gotten their city planning right in terms of minimizing CO2 emissions.

He noted that of Singapore's 4.6 million population, 1.6 million use the rapid transit systems daily while 3 million use the island state's comprehensive bus system.

"It's a city where you don't need a car because you can travel around easily and relatively cheaply," he said. (dpa)